Method of cutting a substrate, method of processing a wafer-like object, and method of manufacturing a semiconductor device

ABSTRACT

A laser beam machining method and a laser beam machining device capable of cutting a work without producing a fusing and a cracking out of a predetermined cutting line on the surface of the work, wherein a pulse laser beam is radiated on the predetermined cut line on the surface of the work under the conditions causing a multiple photon absorption and with a condensed point aligned to the inside of the work, and a modified area is formed inside the work along the predetermined determined cut line by moving the condensed point along the predetermined cut line, whereby the work can be cut with a rather small force by cracking the work along the predetermined cut line starting from the modified area and, because the pulse laser beam radiated is not almost absorbed onto the surface of the work, the surface is not fused even if the modified area is formed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuing application of PCT Application No.PCT/JP01/07954 filed on Sep. 13, 2001, designating U.S.A. and nowpending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to laser processing methods and laserprocessing apparatus used for cutting objects to be processed such assemiconductor material substrates, piezoelectric material substrates,and glass substrates.

2. Related Background Art

One of laser applications is cutting. A optical cutting process effectedby laser is as follows: For embodiment, a part to be cut in an object tobe processed such as a semiconductor wafer or glass substrate isirradiated with laser light having a wavelength absorbed by the object,so that melting upon heating proceeds due to the laser light absorptionfrom the surface to rear face of the object to be processed at the partto be cut, whereby the object to be processed is cut. However, thismethod also melts surroundings of the region to become the cutting partin the surface of the object to be cut. Therefore, in the case where theobject to be processed is a semiconductor wafer, semiconductor deviceslocated near the above-mentioned region among those formed in thesurface of the semiconductor wafer might melt. In the specification,“wafer shape” means a shape similar to a semiconductor wafer made ofsilicon of which thickness is about 100 μm, for example, a thin circularshape having a orientation flat therein.

Known as embodiments of methods which can prevent the surface of theobject to be processed from melting are laser-based cutting methodsdisclosed in Japanese Patent Application Laid-Open No. 2000-219528 andJapanese Patent Application Laid-Open No. 2000-15467. In the cuttingmethods of these publications, the part to be cut in the object to beprocessed is heated with laser light, and then the object is cooled, soas to generate a thermal shock in the part to be cut in the object,whereby the object is cut.

When the thermal shock generated in the object to be processed is largein the cutting methods of the above-mentioned publications, unnecessaryfractures such as those deviating from lines along which the object isintended to be cut or those extending to a part not irradiated withlaser may occur. Therefore, these cutting methods cannot achieveprecision cutting. When the object to be processed is a semiconductorwafer, a glass substrate formed with a liquid crystal display device, ora glass substrate formed with an electrode pattern in particular,semiconductor chips, liquid crystal display devices, or electrodepatterns may be damaged due to the unnecessary fractures. Also, averageinput energy is so high in these cutting methods that the thermal damageimparted to the semiconductor chip and the like is large.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide laser processingmethods and laser processing apparatus which generate no unnecessaryfractures in the surface of an object to be processed and do not meltthe surface.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating an object to be processed withlaser light with a light-converging point located therewithin, so as toform a modified region caused by multiphoton absorption within theobject along a cutting line along which the object should be cut. Ifthere is a certain start region in the part to be cut in the object tobe processed, the object to be processed can be broken by a relativelysmall force so as to be cut. In the laser processing method inaccordance with this aspect of the present invention, the object to beprocessed is broken along the line along which the object is intended tobe cut using the modified region as the starting point, whereby theobject can be cut. Hence, the object to be processed can be cut with arelatively small force, whereby the object can be cut without generatingunnecessary fractures deviating from the line along which the object isintended to be cut in the surface of the object.

The laser processing method in accordance with this aspect of thepresent invention locally generates multiphoton absorption within theobject to be processed, thereby forming a modified region. Therefore,laser light is hardly absorbed by the surface of the object to beprocessed, whereby the surface of the object will not melt. Here, thelight-converging point refers to the position where the laser light isconverged. The line along which the object is intended to be cut may bea line actually drawn on the surface or inside of the object to be cutor a virtual line.

The laser processing method in accordance with an aspect the presentinvention comprises a step of irradiating an object to be processed withlaser light with a light-converging point located therewithin under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 μs or less at the light-converging point, so as to forma modified region caused by multiphoton absorption within the objectalong a line along which the object is intended to be cut in the object.

The laser processing method in accordance with this aspect of thepresent invention irradiates an object to be processed with laser lightwith a light-converging point located therewithin under a condition witha peak power density of at least 1×10⁸ (W/cm²) and a pulse width of 1 μsor less at the light-converging point. Therefore, a phenomenon known asoptical damage caused by multiphoton absorption occurs within the objectto be processed. This optical damage induces thermal distortion withinthe object to be processed, thereby forming a crack region within theobject to be processed. The crack region is an embodiment of theabove-mentioned modified region, whereby the laser processing method inaccordance with this aspect of the present invention enables laserprocessing without generating melt or unnecessary fractures deviatingfrom the line along which the object is intended to be cut in thesurface of the object. An embodiment of the object to be processed inthis laser processing method is a member including glass. Here, the peakpower density refers to the electric field intensity of pulse laserlight at the light-converging point.

The laser processing method in accordance with an aspect the presentinvention comprises a step of irradiating an object to be processed withlaser light with a light-converging point located therewithin under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 μs or less at the light-converging point, so as to forma modified region including a molten processed region within the objectalong a line along which the object is intended to be cut in the object.

The laser processing method in accordance with this aspect of thepresent invention irradiates an object to be processed with laser lightwith a light-converging point located therewithin under a condition witha peak power density of at least 1×10⁸ (W/cm²) and a pulse width of 1 μsor less at the light-converging point. Therefore, the inside of theobject to be processed is locally heated by multiphoton absorption. Thisheating forms a molten processed region within the object to beprocessed. The molten processed region is an embodiment of theabove-mentioned modified region, whereby the laser processing method inaccordance with this aspect of the present invention enables laserprocessing without generating melt or unnecessary fractures deviatingfrom the line along which the object is intended to be cut in thesurface of the object. An embodiment of the object to be processed inthis laser processing method is a member including a semiconductormaterial.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating an object to be processed withlaser light with a light-converging point located therewithin under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 ns or less at the light-converging point, so as to forma modified region including a refractive index change region which is aregion with a changed refractive index within the object along a linealong which the object is intended to be cut in the object.

The laser processing method in accordance with this aspect of thepresent invention irradiates an object to be processed with laser lightwith a light-converging point located therewithin under a condition witha peak power density of at least 1×10⁸ (W/cm²) and a pulse width of 1 nsor less at the light-converging point. When multiphoton absorption isgenerated within the object to be processed with a very short pulsewidth as in this aspect of the present invention, the energy caused bymultiphoton absorption is not transformed into thermal energy, so that apermanent structural change such as ionic valence change,crystallization, or polarization orientation is induced within theobject, whereby a refractive index change region is formed. Thisrefractive index change region is an embodiment of the above-mentionedmodified region, whereby the laser processing method in accordance withthis aspect of the present invention enables laser processing withoutgenerating melt or unnecessary fractures deviating from the line alongwhich the object is intended to be cut in the surface of the object. Anembodiment of the object to be processed in this laser processing methodis a member including glass.

Modes employable in the foregoing laser processing methods in accordancewith the present invention are as follows: Laser light emitted from alaser light source can include pulse laser light. The pulse laser lightcan concentrate the energy of laser spatially and temporally, wherebyeven a single laser light source allows the electric field intensity(peak power density) at the light-converging point of laser light tohave such a magnitude that multiphoton absorption can occur.

Irradiating the object to be processed with a light-converging pointlocated therewithin can encompass a case where laser light emitted fromone laser light source is converged and then the object is irradiatedwith thus converged laser light with a light-converging point locatedtherewithin, for embodiment. This converges laser light, therebyallowing the electric field intensity of laser light at thelight-converging point to have such a magnitude that multiphotonabsorption can occur.

Irradiating the object to be processed with a light-converging pointlocated therewithin can encompass a case where the object to beprocessed is irradiated with respective laser light beams emitted from aplurality of laser light sources from directions different from eachother with a light-converging point located therewithin. Since aplurality of laser light sources are used, this allows the electricfield intensity of laser light at the light-converging point to havesuch a magnitude that multiphoton absorption can occur. Hence, evencontinuous wave laser light having an instantaneous power lower thanthat of pulse laser light can form a modified region. The respectivelaser light beams emitted from a plurality of laser light sources mayenter the object to be processed from the surface thereof. A pluralityof laser light sources may include a laser light source for emittinglaser light entering the object to be processed from the surfacethereof, and a laser light source for emitting laser light entering theobject to be processed from the rear face thereof. A plurality of laserlight sources may include a light source section in which laser lightsources are arranged in an array along a line along which the object isintended to be cut. This can form a plurality of light-converging pointsalong the line along which the object is intended to be cut at the sametime, thus being able to improve the processing speed.

The modified region is formed by moving the object to be processedrelative to the light-converging point of laser light located within theobject. Here, the above-mentioned relative movement forms the modifiedregion within the object to be processed along a line along which theobject is intended to be cut on the surface of the object.

The method may further comprise a cutting step of cutting the object tobe processed along the line along which the object is intended to becut. When the object to be processed cannot be cut in the modifiedregion forming step, the cutting step cuts the object. The cutting stepbreaks the object to be processed using the modified region as astarting point, thus being able to cut the object with a relativelysmall force. This can cut the object to be processed without generatingunnecessary fractures deviating from the line along which the object isintended to be cut in the surface of the object.

Embodiments of the object to be processed are members including glass,piezoelectric material, and semiconductor material. Another embodimentof the object to be processed is a member transparent to laser lightemitted. This laser processing method is also applicable to an object tobe processed having a surface formed with an electronic device orelectrode pattern. The electronic device refers to a semiconductordevice, a display device such as liquid crystal, a piezoelectric device,or the like.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating a semiconductor material withlaser light with a light-converging point located therewithin under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 μs or less at the light-converging point, so as to forma modified region within the semiconductor material along a line alongwhich the object is intended to be cut in the semiconductor material.The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating a piezoelectric material withlaser light with a light-converging point located therewithin under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 μs or less at the light-converging point, so as to forma modified region within the piezoelectric material along a line alongwhich the object is intended to be cut in the piezoelectric material.These methods enable laser cutting without generating melt orunnecessary fractures deviating from the line along which the object isintended to be cut in the surface of the object to be processed for thesame reason as that in the laser processing methods in accordance withthe foregoing aspects of the present invention.

In the laser processing method in accordance with an aspect of thepresent invention, the object to be processed may have a surface formedwith a plurality of circuit sections, while a light-converging point oflaser light is located in the inside of the object to be processedfacing a gap formed between adjacent circuit sections in the pluralityof circuit sections. This can reliably cut the object to be processed atthe position of the gap formed between adjacent circuit sections.

The laser processing method in accordance with an aspect of the presentinvention can converge laser light at an angle by which a plurality ofcircuit sections are not irradiated with the laser light. This canprevent the laser light from entering the circuit sections and protectthe circuit sections against the laser light.

The laser processing method in accordance with an aspect the presentinvention comprises a step of irradiating a semiconductor material withlaser light with a light-converging point located within thesemiconductor material, so as to form a molten processed region onlywithin the semiconductor material along a line along which the object isintended to be cut in the semiconductor material. The laser processingmethod in accordance with this aspect of the present invention enableslaser processing without generating unnecessary fractures in the surfaceof the object to be processed and without melting the surface due to thesame reasons as mentioned above. The molten processed region may becaused by multiphoton absorption or other reasons.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating an object to be processed withlaser light such that a light-converging point of laser lightelliptically polarized with an ellipticity of other than 1 is locatedwithin the object to be processed while the major axis of an ellipseindicative of the elliptical polarization of the laser light extendsalong a line along which the object is intended to be cut, so as to forma modified region caused by multiphoton absorption along the line alongwhich the object is intended to be cut within the object to beprocessed.

The laser processing method in accordance with this aspect of thepresent invention forms a modified region by irradiating the object tobe processed with laser light such that the major axis of an ellipseindicative of the elliptical polarization of laser light extends alongthe line along which the object is intended to be cut in the object tobe processed. The inventor has found that, when elliptically polarizedlaser light is used, the forming of a modified region is accelerated inthe major axis direction of an ellipse indicative of the ellipticalpolarization (i.e., the direction in which the deviation in polarizationis strong). Therefore, when a modified region is formed by irradiatingthe object to be processed with laser light such that the major axisdirection of the ellipse indicative of the elliptical polarizationextends along the line along which the object is intended to be cut inthe object to be processed, the modified region extending along the linealong which the object is intended to be cut can be formed efficiently.Therefore, the laser processing method in accordance with this aspect ofthe present invention can improve the processing speed of the object tobe processed.

Also, the laser processing method in accordance with the presentinvention restrains the modified region from being formed except in thedirection extending along the line along which the object is intended tobe cut, thus making it possible to cut the object to be processedprecisely along the line along which the object is intended to be cut.

Here, the ellipticity refers to half the length of the minor axis/halfthe length of major axis of the ellipse. As the ellipticity of laserlight is smaller, the forming of modified region is accelerated in thedirection extending along the line along which the object is intended tobe cut but suppressed in the other directions. The ellipticity can bedetermined in view of the thickness, material, and the like of theobject to be processed. Linear polarization is elliptical polarizationwith an ellipticity of zero.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating an object to be processed withlaser light such that a light-converging point of laser lightelliptically polarized with an ellipticity of other than 1 is locatedwithin the object to be processed while the major axis of an ellipseindicative of the elliptical polarization of the laser light extendsalong a line along which the object is intended to be cut under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 μs or less at the light-converging point, so as to forma modified region including a crack region along the line along whichthe object is intended to be cut within the object to be processed.

The laser processing method in accordance with this aspect of thepresent invention irradiates the object to be processed with laser lightsuch that the major axis of the ellipse indicative of the ellipticalpolarization of laser light extends along the line along which theobject is intended to be cut in the object to be processed, thus makingit possible to form the modified region efficiently and cut the objectprecisely along the line along which the object is intended to be cut asin the laser processing method in accordance with the above-mentionedaspect of the present invention.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating an object to be processed withlaser light such that a light-converging point of laser lightelliptically polarized with an ellipticity of other than 1 is locatedwithin the object to be processed while the major axis of an ellipseindicative of the elliptical polarization of the laser light extendsalong the line along which the object is intended to be cut under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 μs or less at the light-converging point, so as to forma modified region including a molten processed region along the linealong which the object is intended to be cut within the object to beprocessed.

The laser processing method in accordance with this aspect of thepresent invention irradiates the object to be processed with laser lightsuch that the major axis of the ellipse indicative of the ellipticalpolarization of laser light extends along the line along which theobject is intended to be cut in the object to be processed, thus makingit possible to form the modified region efficiently and cut the objectprecisely along the line along which the object is intended to be cut asin the laser processing method in accordance with the above-mentionedaspect of the present invention.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating an object to be processed withlaser light such that a light-converging point of laser lightelliptically polarized with an ellipticity of other than 1 is locatedwithin the object to be processed while the major axis of an ellipseindicative of the elliptical polarization of the laser light extendsalong a line along which the object is intended to be cut under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 ns or less at the light-converging point, so as to forma modified region including a refractive index change region which is aregion with a changed refractive index within the object along a linealong which the object is intended to be cut in the object.

The laser processing method in accordance with this aspect of thepresent invention irradiates the object to be processed with laser lightsuch that the major axis of the ellipse indicative of the ellipticalpolarization of laser light extends along the line along which theobject is intended to be cut in the object to be processed, thus makingit possible to form the modified region efficiently and cut the objectprecisely along the line along which the object is intended to be cut asin the laser processing method in accordance with the above-mentionedaspect of the present invention.

Modes employable in the laser processing methods in accordance with theforegoing aspects of the present invention are as follows:

Laser light having elliptical polarization with an ellipticity of zerocan be used. Linearly polarized light is obtained when the ellipticityis zero. Linearly polarized light can maximize the size of the modifiedregion extending along the line along which the object is intended to becut and minimize the sizes in the other directions. The ellipticity ofelliptically polarized light can be adjusted by the angle of directionof a quarter-wave plate. When a quarter-wave plate is used, theellipticity can be adjusted by changing the angle of direction alone.

After the step of forming the modified region, the object to beprocessed may be irradiated with laser light while the polarization oflaser light is rotated by about 90° by a half-wave plate. Also, afterthe step of forming the modified region, the object to be processed maybe irradiated with laser light while the object to be processed isrotated by about 90° about the thickness direction of the object to beprocessed. These can form another modified region extending in adirection along the surface of the object to be processed andintersecting the former modified region. Therefore, for embodiment,respective modified regions extending along lines along which the objectis intended to be cut in X- and Y-axis directions can be formedefficiently.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating an object to be processed withlaser light such that a light-converging point of laser lightelliptically polarized with an ellipticity of other than 1 is locatedwithin the object to be processed while the major axis of an ellipseindicative of the elliptical polarization of the laser light extendsalong a line along which the object is intended to be cut, so as to cutthe object to be processed along the line along which the object isintended to be cut.

The laser processing method in accordance with this aspect of thepresent invention irradiates the object to be processed with laser lightsuch that the major axis of the ellipse indicative of the ellipticalpolarization of laser light extends along the line along which theobject is intended to be cut in the object to be processed. Therefore,the object to be processed can be cut along the line along which theobject is intended to be cut. The laser processing method in accordancewith this aspect of the present invention can cut the object to beprocessed by making the object absorb laser light so as to melt theobject upon heating. Also, the laser processing method in accordancewith this aspect of the present invention may generate multiphotonabsorption by irradiating the object to be processed with laser light,thereby forming a modified region within the object, and cut the objectwhile using the modified region as a starting point.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; ellipticity adjustingmeans for making the pulse laser light emitted from the laser lightsource attain elliptical polarization with an ellipticity of other than1; major axis adjusting means for making a major axis of an ellipseindicative of the elliptical polarization of the pulse laser lightadjusted by the ellipticity adjusting means extend along a line alongwhich the object is intended to be cut in an object to be processed;light-converging means for converging the pulse laser light adjusted bythe major axis adjusting means such that the pulse laser light attains apeak power density of at least 1×10⁸ (W/cm²) at a light-convergingpoint; means for locating the light-converging point of the pulse laserlight converged by the light-converging point within the object to beprocessed; and moving means for relatively moving the light-convergingpoint of pulse laser light along the line along which the object isintended to be cut.

The laser processing apparatus in accordance with this aspect of thepresent invention enables laser cutting without generating melt orunnecessary fractures deviating from the line along which the object isintended to be cut in the surface of the object to be processed for thesame reason as that in the laser processing methods in accordance withthe above-mentioned aspects of the present invention. Also, itirradiates the object to be processed with laser light such that themajor axis of the ellipse indicative of the elliptical polarization oflaser light extends along the line along which the object is intended tobe cut in the object to be processed, thus making it possible to formthe modified region efficiently and cut the object precisely along theline along which the object is intended to be cut with the laserprocessing methods in accordance with the above-mentioned aspects of thepresent invention.

Modes employable in the laser processing apparatus in accordance withthe present invention are as follows:

It may comprise 90° rotation adjusting means adapted to rotate thepolarization of the pulse laser light adjusted by the ellipticityadjusting means by about 90°. Also, it may comprise rotating means forrotating a table for mounting the object to be processed by about 90°about a thickness direction of the object. These can make the major axisof the ellipse indicative of the elliptical polarization of pulse laserlight extend along another line along which the object is intended to becut which extends in a direction along a surface of the object to beprocessed while extending in a direction intersecting along the formerline along which the object is intended to be cut. Therefore, forembodiment, respective modified regions extending along lines alongwhich the object is intended to be cut in X- and Y-axis directions canbe formed efficiently.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less and linearpolarization; linear polarization adjusting means for making thedirection of linear polarization of the pulse laser light emitted fromthe laser light source align with a line along which the object isintended to be cut in an object to be processed; light-converging meansfor converging the pulse laser light adjusted by the linear polarizationadjusting means such that the pulse laser light attains a peak powerdensity of at least 1×10⁸ (W/cm²) at a light-converging point; means forlocating the light-converging point of the pulse laser light convergedby the light-converging point within the object to be processed; andmoving means for relatively moving the light-converging point of pulselaser light along the line along which the object is intended to be cut.

The laser processing apparatus in accordance with this aspect of thepresent invention enables laser cutting without generating melt orunnecessary fractures deviating from the line along which the object isintended to be cut in the surface of the object to be processed for thesame reason as that in the laser processing methods in accordance withthe above-mentioned aspects of the present invention. Also, as with thelaser processing methods in accordance with the above-mentioned aspectsof the present invention, the laser processing apparatus in accordancewith this aspect of the present invention makes it possible to form themodified region efficiently and cut the object precisely along the linealong which the object is intended to be cut.

(3) The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; power adjusting meansfor adjusting the magnitude of power of the pulse laser light emittedfrom the laser light source according to an input of the magnitude ofpower of pulse laser light; light-converging means for converging thepulse laser light adjusted by the linear polarization adjusting meanssuch that the pulse laser light attains a peak power density of at least1×10⁸ (W/cm²) at a light-converging point; means for locating thelight-converging point of the pulse laser light converged by thelight-converging means within an object to be processed; and movingmeans for relatively moving the light-converging point of pulse laserlight along a line along which the object is intended to be cut in theobject to be processed; wherein one modified spot is formed within theobject to be processed by irradiating the object to be processed withone pulse of pulse laser light while locating the light-converging pointwithin the object; the laser processing apparatus further comprisingcorrelation storing means having stored therein a correlation betweenthe magnitude of power of pulse laser adjusted by the power adjustingmeans and the size of modified spot; size selecting means for choosing,according to an inputted magnitude of power of pulse laser light, a sizeof the modified spot formed at this magnitude of power from thecorrelation storing means; and size display means for displaying thesize of modified spot chosen by the size selecting means.

The inventor has found that the modified spot can be controlled so as tobecome smaller and larger when the power of pulse laser light is madelower and higher, respectively. The modified spot is a modified partformed by one pulse of pulse laser light, whereas an assembly ofmodified spots forms a modified region. Control of the modified spotsize affects cutting of the object to be processed. Namely, the accuracyin cutting the object to be processed along the line along which theobject is intended to be cut and the flatness of the cross sectiondeteriorate when the modified spot is too large. When the modified spotis too small for the object to be processed having a large thickness, onthe other hand, the object is hard to cut. The laser processingapparatus in accordance with this aspect of the present invention cancontrol the size of modified spot by adjusting the magnitude of power ofpulse laser light. Therefore, it can cut the object to be processedprecisely along the line along which the object is intended to be cut,and can obtain a flat cross section.

The laser processing apparatus in accordance with this aspect of thepresent invention also comprises correlation storing means having storedtherein a correlation between the magnitude of power of pulse laseradjusted by the power adjusting means and the size of modified spot.According to an inputted magnitude of power of pulse laser light, thesize of modified spot formed at this magnitude of power is chosen fromthe correlation storing means, and thus chosen size of modified spot isdisplayed. Therefore, the size of modified spot formed at the magnitudeof power of pulse laser light fed into the laser processing apparatuscan be seen before laser processing.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; a light-converginglens for converging the pulse laser light emitted from the laser lightsource such that the pulse laser light attains a peak power density ofat least 1×10⁸ (W/cm²) at a light-converging point; numerical apertureadjusting means for adjusting the size of numerical aperture of anoptical system including the light-converging lens according to aninputted size of numerical aperture; means for locating thelight-converging point of the pulse laser light converged by thelight-converging lens within an object to be processed; and moving meansfor relatively moving the light-converging point of pulse laser lightalong a line along which the object is intended to be cut in the objectto be processed; wherein one modified spot is formed within the objectto be processed by irradiating the object to be processed with one pulseof pulse laser light while locating the light-converging point withinthe object; the laser processing apparatus further comprisingcorrelation storing means having stored therein a correlation betweenthe size of numerical aperture adjusted by the power adjusting means andthe size of modified spot; size selecting means for choosing, accordingto an inputted magnitude of power of pulse laser light, a size of themodified spot formed at this size of numerical aperture from thecorrelation storing means; and size display means for displaying thesize of modified spot chosen by the size selecting means.

The inventor has found that the modified spot can be controlled so as tobecome smaller and larger when the numerical aperture of the opticalsystem including the light-converging lens is made greater and smaller,respectively. Thus, the laser processing apparatus in accordance withthis aspect of the present invention can control the size of modifiedspot by adjusting the size of numerical aperture of the optical systemincluding the light-converging lens.

The laser processing apparatus in accordance with this aspect of thepresent invention also comprises correlation storing means having storedtherein a correlation between the size of numerical aperture and thesize of modified spot. According to an inputted size of numericalaperture, the size of modified spot formed at this magnitude of power ischosen from the correlation storing means, and thus chosen size ofmodified spot is displayed. Therefore, the size of modified spot formedat the size of numerical aperture fed into the laser processingapparatus can be seen before laser processing.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; and lens selectingmeans including a plurality of light-converging lenses for convergingthe pulse laser light emitted from the laser light source such that thepulse laser light attains a peak power density of at least 1×10⁸ (W/cm²)at a light-converging point, the lens selecting means being adapted toselect among a plurality of light-converging lenses, a plurality ofoptical systems including the light-converging lenses having respectivenumerical apertures different from each other; means for locating thelight-converging point of the pulse laser light converged by alight-converging lens chosen by the lens selecting means within anobject to be processed; and moving means for relatively moving thelight-converging point of pulse laser light along a line along which theobject is intended to be cut in the object to be processed; wherein onemodified spot is formed within the object to be processed by irradiatingthe object to be processed with one pulse of pulse laser light whilelocating the light-converging point within the object; the laserprocessing apparatus further comprising correlation storing means havingstored therein a correlation between sizes of numerical apertures of aplurality of optical systems including the light-converging lenses andthe size of modified spot; size selecting means for choosing, accordingto a size of numerical aperture of an optical system including a chosenlight-converging lens, a size of the modified spot formed at this sizeof numerical aperture from the correlation storing means; and sizedisplay means for displaying the size of modified spot chosen by thesize selecting means.

The laser processing apparatus in accordance with the present inventioncan control the size of modified spot. Also, the size of modified spotformed at the size of numerical aperture of the optical system includingthe chosen light-converging lens can be seen before laser processing.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; power adjusting meansfor adjusting the magnitude of power of pulse laser light emitted fromthe laser light source according to an inputted magnitude of power ofpulse laser light; a light-converging lens for converging the pulselaser light emitted from the laser light source such that the pulselaser light attains a peak power density of at least 1×10⁸ (W/cm²) at alight-converging point; numerical aperture adjusting means for adjustingthe size of numerical aperture of an optical system including thelight-converging lens according to an inputted size of numericalaperture; means for locating the light-converging point of the pulselaser light converged by the light-converging lens within an object tobe processed; and moving means for relatively moving thelight-converging point of pulse laser light along a line along which theobject is intended to be cut in the object to be processed; wherein onemodified spot is formed within the object to be processed by irradiatingthe object to be processed with one pulse of pulse laser light whilelocating the light-converging point within the object; the laserprocessing apparatus further comprising correlation storing means havingstored therein a correlation between a set of the magnitude of power ofpulse laser light adjusted by the power adjusting means and the size ofnumerical aperture adjusted by the numerical aperture adjusting meansand the size of modified spot; size selecting means for choosing,according to an inputted magnitude of power of pulse laser light and aninputted size of numerical aperture, a size of the modified spot formedat thus inputted magnitude and size; and size display means fordisplaying the size of modified spot chosen by the size selecting means.

The laser processing apparatus in accordance with this aspect of thepresent invention can combine power adjustment with numerical apertureadjustment, thus being able to increase the number of kinds ofcontrollable dimensions of modified spots. Also, for the same reason asthat of the laser processing apparatus in accordance with the presentinvention, the size of modified spot can be seen before laserprocessing.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; power adjusting meansfor adjusting the magnitude of power of pulse laser light emitted fromthe laser light source according to an inputted magnitude of power ofpulse laser light; lens selecting means including a plurality oflight-converging lenses for converging the pulse laser light emittedfrom the laser light source such that the pulse laser light attains apeak power density of at least 1×10⁸ (W/cm²) at a light-convergingpoint, the lens selecting means being adapted to select among aplurality of light-converging lenses, a plurality of optical systemsincluding the light-converging lenses having respective numericalapertures different from each other; means for locating thelight-converging point of the pulse laser light converged by alight-converging lens chosen by the lens selecting means within anobject to be processed; and moving means for relatively moving thelight-converging point of pulse laser light along a line along which theobject is intended to be cut in the object to be processed; wherein onemodified spot is formed within the object to be processed by irradiatingthe object to be processed with one pulse of pulse laser light whilelocating the light-converging point within the object; the laserprocessing apparatus further comprising correlation storing means havingstored there in a correlation between a set of the magnitude of power ofpulse laser light adjusted by the power adjusting means and sizes ofnumerical apertures of a plurality of optical systems including thelight-converging lenses and the size of modified spot; size selectingmeans for choosing, according to an inputted magnitude of power of pulselaser light and an inputted size of numerical aperture, a size of themodified spot formed at thus inputted magnitude and size; and sizedisplay means for displaying the size of modified spot chosen by thesize selecting means.

For the same reason as that of the laser processing apparatus inaccordance with the above-mentioned aspect of the present invention, thelaser processing apparatus in accordance with this aspect of the presentinvention can increase the number of kinds of controllable dimensions ofmodified spots and can see the size of modified spots before laserprocessing.

The laser processing apparatus explained in the foregoing may compriseimage preparing means for preparing an image of modified spot having thesize selected by the size selecting means, and image display means fordisplaying the image prepared by the image preparing means. This allowsthe formed modified spot to be grasped visually before laser processing.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; power adjusting meansfor adjusting the magnitude of power of pulse laser light emitted fromthe laser light source; light-converging means for converging the pulselaser light emitted from the laser light source such that the pulselaser light attains a peak power density of at least 1×10⁸ (W/cm²) at alight-converging point; means for locating the light-converging point ofthe pulse laser light converged by the light-converging means within anobject to be processed; and moving means for relatively moving thelight-converging point of pulse laser light along a line along which theobject is intended to be cut in the object to be processed; wherein onemodified spot is formed within the object to be processed by irradiatingthe object to be processed with one pulse of pulse laser light whilelocating the light-converging point within the object; the laserprocessing apparatus further comprising correlation storing means havingstored therein a correlation between the magnitude of power of pulselaser light adjusted by the power adjusting means and the size ofmodified spot; power selecting means for choosing, according to aninputted size of modified spot, a magnitude of power of pulse laserlight adapted to form this size from the correlation storing means; thepower adjusting means adjusting the magnitude of power of pulse laserlight emitted from the laser light source such that the magnitude ofpower chosen by the power selecting means is attained.

The laser processing apparatus in accordance with this aspect of thepresent invention comprises correlation storing means having storedtherein the magnitude of power of pulse laser light and the size ofmodified spot. According to an inputted size of the modified spot, themagnitude of power of pulse laser light adapted to form this size ischosen from the correlation storing means. The power adjusting meansadjusts the magnitude of power of pulse laser light emitted from thelaser light source so as to make it become the magnitude of power chosenby the power selecting means. Therefore, a modified spot having adesirable size can be formed.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; a light-converginglens for converging the pulse laser light emitted from the laser lightsource such that the pulse laser light attains a peak power density ofat least 1×10⁸ (W/cm²) at a light-converging point; numerical apertureadjusting means for adjusting the size of numerical aperture of anoptical system including the light-converging lens according to aninputted size of numerical aperture; means for locating thelight-converging point of the pulse laser light converged by thelight-converging lens within an object to be processed; and moving meansfor relatively moving the light-converging point of pulse laser lightalong a line along which the object is intended to be cut in the objectto be processed; wherein one modified spot is formed within the objectto be processed by irradiating the object to be processed with one pulseof pulse laser light while locating the light-converging point withinthe object; the laser processing apparatus further comprisingcorrelation storing means having stored therein a correlation betweenthe size of numerical aperture adjusted by the numerical apertureadjusting means and the size of modified spot; and numerical apertureselecting means for choosing, according to an inputted size of modifiedspot, the size of numerical aperture adapted to form thus inputted size;the numerical aperture adjusting means adjusting the size of numericalaperture of the optical system including the light-converging lens suchthat the size of numerical aperture chosen by the numerical apertureselecting means is attained.

The laser processing apparatus in accordance with this aspect of thepresent invention comprises correlation storing means having storedtherein the size of numerical aperture and the size of modified spot.According to an inputted size of modified spot, the size of numericalaperture adapted to form thus inputted size is chosen from thecorrelation storing means. The numerical aperture adjusting meansadjusts the size of numerical aperture of the optical system includingthe light-converging lens such that the size of numerical aperturechosen by the numerical aperture selecting means is attained. Therefore,modified spots having a desirable size can be formed.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; lens selecting meansincluding a plurality of light-converging lenses for converging thepulse laser light emitted from the laser light source such that thepulse laser light attains a peak power density of at least 1×10⁸ (W/cm²)at a light-converging point, the lens selecting means being adapted toselect among a plurality of light-converging lenses, a plurality ofoptical systems including the light-converging lenses having respectivenumerical apertures different from each other; means for locating thelight-converging point of the pulse laser light converged by alight-converging lens chosen by the lens selecting means within anobject to be processed; and moving means for relatively moving thelight-converging point of pulse laser light along a line along which theobject is intended to be cut in the object to be processed; wherein onemodified spot is formed within the object to be processed by irradiatingthe object to be processed with one pulse of pulse laser light whilelocating the light-converging point within the object; the laserprocessing apparatus further comprising correlation storing means havingstored therein a correlation between sizes of numerical apertures of aplurality of light-converging lenses and the size of modified spot; andnumerical aperture selecting means for choosing, according to aninputted size of modified spot, a size of numerical aperture adapted toform thus inputted size; the lens selecting means selecting among aplurality of light-converging lenses such that the size of numericalaperture chosen by the numerical aperture selecting means is attained.

According to an inputted size of modified spot, the laser processingapparatus in accordance with this aspect of the present inventionchooses the size of numerical aperture adapted to form thus inputtedsize. The lens selecting means selects among a plurality oflight-converging lenses such that the size of numerical aperture chosenby the numerical aperture selecting means is attained. Therefore,modified spots having a desirable spots can be formed.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; power adjusting meansfor adjusting the magnitude of power of pulse laser light emitted fromthe laser light source; a light-converging lens for converging the pulselaser light emitted from the laser light source such that the pulselaser light attains a peak power density of at least 1×10⁸ (W/cm²) at alight-converging point; numerical aperture adjusting means for adjustingthe size of numerical aperture of an optical system including thelight-converging lens; means for locating the light-converging point ofthe pulse laser light converged by the light-converging lens within anobject to be processed; and moving means for relatively moving thelight-converging point of pulse laser light along a line along which theobject is intended to be cut in the object to be processed; wherein onemodified spot is formed within the object to be processed by irradiatingthe object to be processed with one pulse of pulse laser light whilelocating the light-converging point within the object; the laserprocessing apparatus further comprising correlation storing means havingstored therein a correlation between a set of the magnitude of power ofpulse laser light adjusted by the power adjusting means and the size ofnumerical aperture adjusted by the numerical aperture adjusting meansand the size of modified spot; and set selecting means for choosing,according to an inputted size of modified spot, a set of the magnitudeof power and size of numerical aperture adapted to form this size; thepower adjusting means and numerical aperture adjusting means adjustingthe magnitude of power of pulse laser light emitted from the laser lightsource and the size of numerical aperture of the optical systemincluding the light-converging lens such that the magnitude of power andsize of numerical aperture chosen by the set selecting means areattained.

According to an inputted size of modified spot, the laser processingapparatus in accordance with this aspect of the present inventionchooses a combination of the magnitude of power and size of numericalaperture adapted to form thus inputted size from the correlation storingmeans. Then, it adjusts the magnitude of power of pulse laser light andthe size of numerical aperture of the optical system including thelight-converging lens so as to attain the chosen magnitude of power andsize of numerical aperture. Therefore, modified spots having a desirablesize can be formed. Also, since the magnitude of power and the size ofnumerical aperture are combined together, the number of kinds ofcontrollable dimensions of modified spots can be increased.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; power adjusting meansfor adjusting the magnitude of power of pulse laser light emitted fromthe laser light source; lens selecting means including a plurality oflight-converging lenses for converging the pulse laser light emittedfrom the laser light source such that the pulse laser light attains apeak power density of at least 1×10⁸ (W/cm²) at a light-convergingpoint, the lens selecting means being adapted to select among aplurality of light-converging lenses, a plurality of optical systemsincluding the light-converging lenses having respective numericalapertures different from each other; means for locating thelight-converging point of the pulse laser light converged by alight-converging lens chosen by the lens selecting means within anobject to be processed; and moving means for relatively moving thelight-converging point of pulse laser light along a line along which theobject is intended to be cut in the object to be processed; wherein onemodified spot is formed within the object to be processed by irradiatingthe object to be processed with one pulse of pulse laser light whilelocating the light-converging point within the object; the laserprocessing apparatus further comprising correlation storing means havingstored therein a correlation between a set of the magnitude of power ofpulse laser light adjusted by the power adjusting means and sizes ofnumerical apertures of a plurality of optical systems including thelight-converging lenses and the size of modified spot; and set selectingmeans for choosing, according to an inputted size of modified spot, aset of the magnitude of power and size of numerical aperture adapted toform thus inputted size from the correlation storing means; the poweradjusting means and lens selecting means adjusting the magnitude ofpower of pulse laser light emitted from the laser light source andselecting among a plurality of light-converging lenses so as to attainthe power and size of numerical aperture chosen by the set selectingmeans.

According to an inputted size of modified spot, the laser processingapparatus in accordance with this aspect of the present inventionchooses a combination of the magnitude of power and size of numericalaperture adapted to form thus inputted size from the correlation storingmeans. It adjusts the magnitude of power of pulse laser light emittedfrom the laser light source and selects among a plurality oflight-converging lenses so as to attain the chosen magnitude of powerand size of numerical aperture, respectively. Therefore, modified spotshaving a desirable size can be formed. Also, since the magnitude ofpower and the size of numerical aperture are combined together, thenumber of kinds of controllable dimensions of modified spots can beincreased.

The laser processing apparatus in accordance with this aspect of thepresent invention may further comprise display means for displaying themagnitude of power chosen by the power selecting means, display meansfor displaying the size of numerical aperture chosen by the numericalaperture selecting means, and display means for displaying the magnitudeof power and size of numerical aperture of the set chosen by the setselecting means. This makes it possible to see the power and numericalaperture when the laser processing apparatus operates according to aninputted size of modified spot.

The laser processing apparatus can form a plurality of modified spotsalong a line along which the object is intended to be cut within theobject to be processed. These modified spots define a modified region.The modified region includes at least one of a crack region where acrack is generated within the object to be processed, a molten processedregion which is melted within the object to be processed, and arefractive index change region where refractive index is changed withinthe object to be processed.

An embodiment of modes of power adjusting means is one including atleast one of an ND filter and a polarization filter. In another mode,the laser light source includes a pumping laser whereas the laserprocessing apparatus comprises driving current controlling means forcontrolling the driving current of the pumping laser. These can adjustthe magnitude of power of pulse laser light. An embodiment of modes ofnumerical aperture adjusting means includes at least one of a beamexpander and an iris diaphragm.

The laser processing method in accordance with an aspect of the presentinvention comprises a first step of irradiating an object to beprocessed with pulse laser light while locating a light-converging pointof the pulse laser light within the object, so as to form a firstmodified region caused by multiphoton absorption within the object alonga first line along which the object is intended to be cut in the object;and a second step of irradiating the object with pulse laser light whilemaking the pulse laser light attain a power higher or lower than that inthe first step and locating the light-converging point of the pulselaser light within the object, so as to form a second modified regioncaused by multiphoton absorption within the object along a second linealong which the object is intended to be cut in the object.

The laser processing method in accordance with an aspect of the presentinvention comprises a first step of irradiating an object to beprocessed with pulse laser light while locating a light-converging pointof the pulse laser light within the object, so as to form a firstmodified region caused by multiphoton absorption within the object alonga first line along which the object is intended to be cut in the object;and a second step of irradiating the object with pulse laser light whilemaking an optical system including a light-converging lens forconverging the pulse laser light attain a numerical aperture greater orsmaller than that in the first step and locating the light-convergingpoint of the pulse laser light within the object, so as to form a secondmodified region caused by multiphoton absorption within the object alonga second line along which the object is intended to be cut in theobject.

When respective directions which are easy to cut and hard to cut existdue to the crystal orientation, for embodiment, the laser processingmethods in accordance with these aspects of the present inventiondecreases the size of modified spot constituting a modified regionformed in the easy-to-cut direction and increases the size of modifiedspot constituting another modified region formed in the hard-to-cutdirection. This can attain a flat cross section in the easy-to-cutdirection and enables cutting in the hard-to-cut direction as well.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; frequency adjustingmeans for adjusting the magnitude of a repetition frequency of the pulselaser light emitted from the laser light source according to an inputtedmagnitude of frequency; light-converging means for converging the pulselaser light emitted from the laser light source such that the pulselaser light attains a peak power density of at least 1×10⁸ (W/cm²) at alight-converging point; means for locating the light-converging point ofthe pulse laser light converged by the light-converging means within anobject to be processed; and moving means for relatively moving thelight-converging point of pulse laser light along a line along which theobject is intended to be cut in the object to be processed; wherein onemodified spot is formed within the object to be processed by irradiatingthe object to be processed with one pulse of pulse laser light whilelocating the light-converging point within the object; and wherein aplurality of modified spots are formed along the line along which theobject is intended to be cut within the object to be processed byirradiating the object to be processed with a plurality of pulses ofpulse laser light while locating the light-converging point within theobject and relatively moving the light-converging point along the linealong which the object is intended to be cut; the laser processingapparatus further comprising distance calculating means for calculatinga distance between modified spots adjacent each other according to aninputted magnitude of frequency; and distance display means fordisplaying the distance calculated by the distance calculating means.

The inventor has found that, when the light-converging point of pulselaser light has a fixed relative moving speed, the distance between amodified part (referred to as modified spot) formed by one pulse ofpulse laser light and a modified spot formed by the next one pulse oflaser light can be made greater by lowering the repetition frequency. Ithas been found that, by contrast, the distance can be made shorter byincreasing the repetition frequency of pulse laser light. In the presentspecification, this distance is expressed as the distance or pitchbetween adjacent modified spots.

Therefore, the distance between the adjacent modified spots can becontrolled by carrying out adjustment for increasing or decreasing therepetition frequency of pulse laser light. Changing the distanceaccording to the kind, thickness, and the like of the object to beprocessed enables cutting in conformity to the object to be processed.Forming a plurality of modified spots along a line along which theobject is intended to be cut within the object to be processed defines amodified region.

The laser processing apparatus in accordance with this aspect of thepresent invention calculates the distance between adjacent modifiedspots according to the inputted magnitude of frequency, and displaysthus calculated distance. Therefore, with respect to modified spotsformed according to the magnitude of frequency fed into the laserprocessing apparatus, the distance between adjacent spots can be seenbefore laser processing.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; light-converging meansfor converging the pulse laser light emitted from the laser light sourcesuch that the pulse laser light attains a peak power density of at least1×10⁸ (W/cm²) at a light-converging point; means for locating thelight-converging point of the pulse laser light converged by thelight-converging means within an object to be processed; moving meansfor relatively moving the light-converging point of pulse laser lightalong a line along which the object is intended to be cut in the objectto be processed; and speed adjusting means for adjusting the magnitudeof relative moving speed of the light-converging point of pulse laserlight caused by the moving means according to an inputted magnitude ofspeed; wherein one modified spot is formed within the object to beprocessed by irradiating the object to be processed with one pulse ofpulse laser light while locating the light-converging point within theobject; and wherein a plurality of modified spots are formed along theline along which the object is intended to be cut within the object tobe processed by irradiating the object to be processed with a pluralityof pulses of pulse laser light while locating the light-converging pointwithin the object and relatively moving the light-converging point alongthe line along which the object is intended to be cut; the laserprocessing apparatus further comprising distance calculating means forcalculating a distance between modified spots adjacent each otheraccording to an inputted magnitude of speed; and distance display meansfor displaying the distance calculated by the distance calculatingmeans.

The inventor has found that, when the light-converging point of pulselaser light has a fixed relative moving speed, the distance betweenadjacent modified spots can be made shorter and longer by decreasing andincreasing the relative moving speed of the light-converging point ofpulse laser light, respectively. Therefore, the distance betweenadjacent modified spots can be controlled by increasing or decreasingthe relative moving speed of the light-converging point of pulse laserlight. As a consequence, a cutting process suitable for an object to beprocessed is possible by changing the distance according to the kind,thickness, and the like of the object to be processed. The relativemovement of the light-converging point of pulse laser light may beachieved by moving the object to be processed while fixing thelight-converging point of pulse laser light, by moving thelight-converging point of pulse laser light while fixing the object tobe processed, or by moving both.

The laser processing apparatus in accordance with this aspect of thepresent invention calculates the distance between adjacent modifiedspots according to the inputted magnitude of speed, and displays thuscalculated distance. Therefore, with respect to modified spots formedaccording to the magnitude of speed fed into the laser processingapparatus, the distance between adjacent spots can be seen before laserprocessing.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; frequency adjustingmeans for adjusting the magnitude of a repetition frequency of the pulselaser light emitted from the laser light source according to an inputtedmagnitude of frequency; light-converging means for converging the pulselaser light emitted from the laser light source such that the pulselaser light attains a peak power density of at least 1×10⁸ (W/cm²) at alight-converging point; means for locating the light-converging point ofthe pulse laser light converged by the light-converging means within anobject to be processed; moving means for relatively moving thelight-converging point of pulse laser light along a line along which theobject is intended to be cut in the object to be processed; and speedadjusting means for adjusting the magnitude of relative moving speed ofthe light-converging point of pulse laser light caused by the movingmeans according to an inputted magnitude of speed; wherein one modifiedspot is formed within the object to be processed by irradiating theobject to be processed with one pulse of pulse laser light whilelocating the light-converging point within the object; and wherein aplurality of modified spots are formed along the line along which theobject is intended to be cut within the object to be processed byirradiating the object to be processed with a plurality of pulses ofpulse laser light while locating the light-converging point within theobject and relatively moving the light-converging point along the linealong which the object is intended to be cut; the laser processingapparatus further comprising distance calculating means for calculatinga distance between modified spots adjacent each other according toinputted magnitudes of frequency and speed; and distance display meansfor displaying the distance calculated by the distance calculatingmeans.

The laser processing apparatus in accordance with this aspect of thepresent invention adjusts both the magnitude of a repetition frequencyof pulse laser light and the magnitude of relative moving speed of thelight-converging point, thereby being able to control the distancebetween adjacent modified spots. Combining these adjustments makes itpossible to increase the number of kinds of controllable dimensionsconcerning the distance. Also, the laser processing apparatus inaccordance with this aspect of the present invention allows the distancebetween adjacent modified spots to be seen before laser processing.

These laser processing apparatus may further comprise size storing meanshaving stored therein the size of a modified spot formed by the laserprocessing apparatus; image preparing means for preparing an image of aplurality of modified spots formed along a line along which the objectis intended to be cut according to the size stored in the sizes to ringmeans and the distance calculated by the distance calculating means; andimage display means for displaying the image prepared by the imagepreparing means. This allows a plurality of modified spots, i.e.,modified region, to be grasped visually before laser processing.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; frequency adjustingmeans for adjusting the magnitude of a repetition frequency of the pulselaser light emitted from the laser light source according to an inputtedmagnitude of frequency; light-converging means for converging the pulselaser light emitted from the laser light source such that the pulselaser light attains a peak power density of at least 1×10⁸ (W/cm²) at alight-converging point; means for locating the light-converging point ofthe pulse laser light converged by the light-converging means within anobject to be processed; and moving means for relatively moving thelight-converging point of pulse laser light along a line along which theobject is intended to be cut in the object to be processed; wherein onemodified spot is formed within the object to be processed by irradiatingthe object to be processed with one pulse of pulse laser light whilelocating the light-converging point within the object; and wherein aplurality of modified spots are formed along the line along which theobject is intended to be cut within the object to be processed byirradiating the object to be processed with a plurality of pulses ofpulse laser light while locating the light-converging point within theobject and relatively moving the light-converging point along the linealong which the object is intended to be cut; the laser processingapparatus further comprising frequency calculating means forcalculating, according to an inputted magnitude of distance betweenmodified spots adjacent each other, the magnitude of repetitionfrequency of the pulse laser light emitted from the laser light sourceso as to attain thus inputted magnitude of distance between the modifiedspots adjacent each other; the frequency adjusting means adjusting themagnitude of repetition frequency of the pulse laser light emitted fromthe laser light source such that the magnitude of frequency calculatedby the frequency calculating means is attained.

According to an inputted magnitude of distance between adjacent modifiedspots, the laser processing apparatus in accordance with this aspect ofthe present invention calculates the magnitude of a repetition frequencyof the pulse laser light emitted from the laser light source such thatthis magnitude of distance is attained between the adjacent modifiedspots. The frequency adjusting means adjusts the magnitude of repetitionfrequency of the pulse laser light emitted from the laser light sourcesuch that the magnitude of frequency calculated by the frequencycalculating means is attained. Therefore, a desirable magnitude ofdistance can be attained between adjacent modified spots.

The laser processing apparatus in accordance with this aspect of thepresent invention may further comprise frequency display means fordisplaying the magnitude of frequency calculated by the frequencycalculating means. When operating the laser processing apparatusaccording to the inputted magnitude of distance between adjacentmodified spots, this allows the frequency to be seen before laserprocessing.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; light-converging meansfor converging the pulse laser light emitted from the laser light sourcesuch that the pulse laser light attains a peak power density of at least1×10⁸ (W/cm²) at a light-converging point; means for locating thelight-converging point of the pulse laser light converged by thelight-converging means within an object to be processed; moving meansfor relatively moving the light-converging point of pulse laser lightalong a line along which the object is intended to be cut in the objectto be processed; and speed adjusting means for adjusting the magnitudeof relative moving speed of the light-converging point caused by themoving means; wherein one modified spot is formed within the object tobe processed by irradiating the object to be processed with one pulse ofpulse laser light while locating the light-converging point within theobject; and wherein a plurality of modified spots are formed along theline along which the object is intended to be cut within the object tobe processed by irradiating the object to be processed with a pluralityof pulses of pulse laser light while locating the light-converging pointwithin the object and relatively moving the light-converging point alongthe line along which the object is intended to be cut; the laserprocessing apparatus further comprising speed calculating means forcalculating, according to an inputted magnitude of distance betweenmodified spots adjacent each other, the magnitude of relative movingspeed of the pulse laser light so as to attain thus inputted magnitudeof distance between the modified spots adjacent each other; the speedadjusting means adjusting the magnitude of relative moving speed of thelight-converging point of pulse laser light caused by the moving meanssuch that the magnitude of relative moving speed calculated by the speedcalculating means is attained.

According to an inputted magnitude of distance between adjacent modifiedspots, the laser processing apparatus in accordance with this aspect ofthe present invention calculates the magnitude of relative moving speedof the light-converging point of pulse laser light caused by the movingmeans. The speed adjusting means adjusts the magnitude of relativemoving speed of the light-converging point of pulse laser light causedby the moving means such that the magnitude of relative moving speedcalculated by the frequency calculating means is attained. Therefore, adesirable magnitude of distance can be attained between adjacentmodified spots.

The laser processing apparatus in accordance with this aspect of thepresent invention may further comprise speed display means fordisplaying the magnitude of relative moving speed calculated by thespeed calculating means. When operating the laser processing apparatusaccording to the inputted magnitude of distance between adjacentmodified spots, this allows the relative moving speed to be seen beforelaser processing.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; frequency adjustingmeans for adjusting the magnitude of a repetition frequency of the pulselaser light emitted from the laser light source; light-converging meansfor converging the pulse laser light emitted from the laser light sourcesuch that the pulse laser light attains a peak power density of at least1×10⁸ (W/cm²) at a light-converging point; means for locating thelight-converging point of the pulse laser light converged by thelight-converging means within an object to be processed; moving meansfor relatively moving the light-converging point of pulse laser lightalong a line along which the object is intended to be cut in the objectto be processed; and speed adjusting means for adjusting the magnitudeof relative moving speed of the light-converging point caused by themoving means; wherein one modified spot is formed within the object tobe processed by irradiating the object to be processed with one pulse ofpulse laser light while locating the light-converging point within theobject; and wherein a plurality of modified spots are formed along theline along which the object is intended to be cut within the object tobe processed by irradiating the object to be processed with a pluralityof pulses of pulse laser light while locating the light-converging pointwithin the object and relatively moving the light-converging point alongthe line along which the object is intended to be cut; the laserprocessing apparatus further comprising combination calculating meansfor calculating, according to an inputted magnitude of distance betweenmodified spots adjacent each other, a combination of the magnitude ofrepetition frequency of the pulse laser light emitted from the laserlight source and the magnitude of relative moving speed of thelight-converging point of pulse laser light caused by the moving meansso as to attain thus inputted magnitude of distance between the modifiedspots adjacent each other; the frequency adjusting means adjusting themagnitude of repetition frequency of the pulse laser light emitted fromthe laser light source such that the magnitude of frequency calculatedby the combination calculating means is attained; the speed adjustingmeans adjusting the magnitude of relative moving speed of thelight-converging point of pulse laser light caused by the moving meanssuch that the magnitude of relative moving speed calculated by thecombination calculating means is attained.

The laser processing apparatus in accordance with this aspect of thepresent invention calculates, according to an inputted magnitude ofdistance between adjacent modified spots, a combination of the magnitudeof repetition frequency of pulse laser light and the relative movingspeed of the light-converging point of pulse laser light such that thusinputted magnitude of distance is attained between the adjacent modifiedspots. The frequency adjusting means and speed adjusting means adjustthe magnitude of repetition frequency and the magnitude of relativemoving speed of the light-converging point of pulse laser light so as toattain the values of calculated combination. Therefore, a desirablemagnitude of distance can be attained between adjacent modified spots.

The laser processing apparatus in accordance with the present inventionmay comprise display means for displaying the magnitude of frequency andmagnitude of relative moving speed calculated by the combinationcalculating means. When operating the laser processing apparatusaccording to the inputted magnitude of distance between adjacentmodified spots, this allows the combination of frequency and relativemoving speed to be seen before laser processing.

The laser processing apparatus in accordance with all the foregoingaspects of the present invention can form a plurality of modified spotsalong a line along which the object is intended to be cut within theobject to be processed. These modified spots define a modified region.The modified region includes at least one of a crack region where acrack is generated within the object to be processed, a molten processedregion which is melted within the object to be processed, and arefractive index change region where refractive index is changed withinthe object to be processed.

The laser processing apparatus in accordance with all the foregoingaspects of the present invention can adjust the distance betweenadjacent modified spots, thereby being able to form a modified regioncontinuously or discontinuously along a line along which the object isintended to be cut. Forming the modified region continuously makes iteasier to cut the object to be processed while using the modified regionas compared with the case where it is not formed continuously. When themodified region is formed discontinuously, the modified region isdiscontinuous along the line along which the object is intended to becut, whereby the part of the line along which the object is intended tobe cut keeps a strength to a certain extent.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating an object to be processed withlaser light while locating a light-converging point of laser lightwithin the object to be processed, so as to form a modified regioncaused by multiphoton absorption within the object along a line alongwhich the object is intended to be cut in the object, and changing theposition of the light-converging point of laser light in the directionof incidence of the laser light irradiating the object to be processedwith respect to the object to be processed, so as to form a plurality ofmodified regions aligning with each other along the direction ofincidence.

By changing the position of the light-converging point of laser lightirradiating the object to be processed in the direction of incidencewith respect to the object to be processed, the laser processing methodin accordance with this aspect of the present invention forms aplurality of modified regions aligning with each other along thedirection of incidence. This can increase the number of positions tobecome starting points when cutting the object to be processed.Therefore, the object to be processed can be cut even in the case wherethe object to be processed has a relatively large thickness and thelike. Embodiments of the direction of incidence include the thicknessdirection of the object to be processed and directions orthogonal to thethickness direction.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating an object to be processed withlaser light while locating a light-converging point of laser lightwithin the object to be processed, so as to form a modified regionwithin the object along a line along which the object is intended to becut in the object, and changing the position of the light-convergingpoint of laser light in the direction of incidence of the laser lightirradiating the object to be processed with respect to the object to beprocessed, so as to form a plurality of modified regions aligning witheach other along the direction of incidence. The laser processing methodin accordance with an aspect of the present invention comprises a stepof irradiating an object to be processed with laser light while locatinga light-converging point of laser light within the object to beprocessed under a condition with a peak power density of at least 1×10⁸(W/cm²) and a pulse width of 1 μs or less at the light-converging point,so as to form a modified region within the object to be processed alonga line along which the object is intended to be cut in the object, andchanging the position of the light-converging point of laser light inthe direction of incidence of the laser light irradiating the object tobe processed with respect to the object to be processed, so as to form aplurality of modified regions aligning with each other along thedirection of incidence.

For the same reason as that in the laser processing methods inaccordance with the foregoing aspects of the present invention, thelaser processing methods in accordance with these aspects of the presentinvention enable laser cutting without generating melt or unnecessaryfractures deviating from the line along which the object is intended tobe cut in the surface of the object to be processed, and can increasethe number of positions to become starting points when cutting theobject to be processed. The modified region may be caused by multiphotonabsorption or other reasons.

The laser processing methods in accordance with these aspects of thepresent invention include the following modes:

A plurality of modified regions may be formed successively from the sidefarther from an entrance face of the object to be processed on whichlaser light irradiating the object to be processed is incident. This canform a plurality of modified regions while in a state where no modifiedregion exists between the entrance face and the light-converging pointof laser light. Therefore, the laser light will not be scattered bymodified regions which have already been formed, whereby each modifiedregion can be formed uniformly.

The modified region includes at least one of a crack region where acrack is generated within the object to be processed, a molten processedregion which is melted within the object to be processed, and arefractive index change region where refractive index is changed withinthe object to be processed.

The laser processing method in accordance with an aspect of the presentinvention comprises a step of irradiating an object to be processed withlaser light while locating a light-converging point of laser lightwithin the object to be processed through a light entrance face of thelaser light with respect to the object to be processed and locating thelight-converging point at a position closer to or farther from theentrance face than is a half thickness position in the thicknessdirection of the object to be processed, so as to form a modified regionwithin the object along a line along which the object is intended to becut in the object.

In the laser processing method in accordance with the present invention,the modified region is formed on the entrance face (e.g., surface) andon the side of the face (e.g., rear face) opposing the entrance facewithin the object to be processed within the object to be processed whenthe light-converging point of laser light is located at a positioncloser to and farther from the entrance face than is a half thicknessposition in the thickness direction, respectively. When a fractureextending along a line along which the object is intended to be cut isgenerated on the surface or rear face of an object to be processed, theobject can be cut easily. The laser processing method in accordance withthis aspect of the present invention can form a modified region on thesurface or rear face side within the object to be processed. This canmake it easier to form the surface or rear face with a fractureextending along the line along which the object is intended to be cut,whereby the object to be processed can be cut easily. As a result, thelaser processing method in accordance with this aspect of the presentinvention enables efficient cutting.

The laser processing method in accordance with this aspect of thepresent invention may be configured such that the entrance face isformed with at least one of an electronic device and an electrodepattern, whereas the light-converging point of laser light irradiatingthe object to be processed is located at a position closer to theentrance face than is the half thickness position in the thicknessdirection. The laser processing method in accordance with this aspect ofthe present invention grows a crack from the modified region toward theentrance face (e.g., surface) and its opposing face (e.g., rear face),thereby cutting the object to be processed. When the modified region isformed on the entrance face side, the distance between the modifiedregion and the entrance face is relatively short, so that the deviationin the growth direction of crack can be made smaller. Therefore, whenthe entrance face of the object to be processed is formed with anelectronic device or an electrode pattern, cutting is possible withoutdamaging the electronic device or the like. The electronic device refersto a semiconductor device, a display device such as liquid crystal, apiezoelectric device, or the like.

The laser processing method in accordance with an aspect of the presentinvention comprises a first step of irradiating an object to beprocessed with pulse laser light while locating a light-converging pointof the pulse laser light within the object, so as to form a firstmodified region caused by multiphoton absorption within the object alonga first line along which the object is intended to be cut in the object;and a second step of irradiating, after the first step, the object withpulse laser light while locating the light-converging point of laserlight at a position different from the light-converging point of laserlight in the first step in the thickness direction of the object to beprocessed within the object, so as to form a second modified regioncaused by multiphoton absorption extending along a second line alongwhich the object is intended to be cut and three-dimensionally crossingthe first modified region within the object.

In a cutting process in which cross-sections of an object to beprocessed cross each other, a modified region and another modifiedregion are not superposed on each other at a location to become thecrossing position between the cross sections in the laser processingmethod in accordance with this aspect of the present invention, wherebythe cutting precision at the crossing position can be prevented fromdeteriorating. This enables cutting with a high precision.

The laser processing method in accordance with this aspect of thepresent invention can form the second modified region closer to theentrance face of the object to be processed with respect to the laserlight than is the first modified region. This keeps the laser lightirradiated at the time of forming the second modified region at thelocation to become the crossing position from being scattered by thefirst modified region, whereby the second modified region can be formeduniformly.

The laser processing methods in accordance with the foregoing aspects ofthe present invention explained in the foregoing have the followingmodes:

When the object to be processed is irradiated with laser light under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 μs or less at the light-converging point, a modifiedregion including a crack region can be formed within the object to beprocessed. This generates a phenomenon of an optical damage caused bymultiphoton absorption within the object to be processed. This opticaldamage induces a thermal distortion within the object to be processed,thereby forming a crack region within the object to be processed. Thiscrack region is an embodiment of the above-mentioned modified region. Anembodiment of the object to be processed in this laser processing methodis a member including glass. The peak power density refers to theelectric field intensity of pulse laser light at the light-convergingpoint.

When the object to be processed is irradiated with laser light under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 μs or less at the light-converging point, a modifiedregion including a molten processed region can be formed within theobject to be processed. Here, the inside of the object to be processedis locally heated by multiphoton absorption. This heating forms a moltenprocessed region within the object to be processed. This moltenprocessed region is an embodiment of the above-mentioned modifiedregion. An embodiment of the object to be processed in this laserprocessing method is a member including a semiconductor material.

When the object to be processed is irradiated with laser light under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 ns or less at the light-converging point, a modifiedregion including a refractive index change region which is a region witha changed refractive index can also be formed within the object to beprocessed. When multiphoton absorption is generated within the object tobe processed with a very short pulse width as such, the energy caused bymultiphoton absorption is not transformed into thermal energy, so that apermanent structural change such as ionic valence change,crystallization, or polarization orientation is induced within theobject, whereby a refractive index change region is formed. Thisrefractive index change region is an embodiment of the above-mentionedmodified region. An embodiment of the object to be processed in thislaser processing method is a member including glass.

Adjustment of the position of the light-converging point of laser lightirradiating the object to be processed in the thickness direction caninclude a first calculating step of defining a desirable position in thethickness direction of the light-converging point of laser lightirradiating the object to be processed as a distance from the entranceface to the inside and dividing the distance by the refractive index ofthe object to be processed with respect to the laser light irradiatingthe object, so as to calculate data of a first relative movement amountof the object in the thickness direction; a second calculating step ofcalculating data of a second relative movement amount of the object inthe thickness direction required for positioning the light-convergingpoint of laser light irradiating the object to be processed at theentrance face; a first moving step of relatively moving the object inthe thickness direction according to the data of second relativemovement amount; and a second moving step of relatively moving theobject in the thickness direction according to the data of firstrelative movement amount after the first moving step. This adjusts theposition of the light-converging point of laser light in the thicknessdirection of the object to be processed at a predetermined positionwithin the object. Namely, with reference to the entrance face, theproduct of the relative movement amount of the object to be processed inthe thickness direction of the object and the refractive index of theobject with respect to the laser light irradiating the object becomesthe distance from the entrance face to the light-converging point oflaser light. Therefore, when the object to be processed is moved by therelative movement amount obtained by dividing the distance from theentrance to the inside of the object by the above-mentioned refractiveindex, the light-converging point of laser light can be aligned with adesirable position in the thickness direction of the object.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; light-converging meansfor converging the pulse laser light emitted from the laser light sourcesuch that the pulse laser light attains a peak power density of at least1×10⁸ (W/cm²) at a light-converging point; first moving means forrelatively moving the light-converging point converged by thelight-converging means along a line along which the object is intendedto be cut in an object to be processed; storing means for storing dataof a first relative movement amount of the object to be processed in thethickness direction for locating the light-converging position of pulselaser light converged by the light-converging means at a desirableposition within the object to be processed, the data of first relativemovement amount being obtained by defining the desirable position as adistance from the entrance face where the pulse laser light emitted fromthe laser light source enters the object to be processed to the insidethereof and dividing the distance by the refractive index of the objectto be processed with respect to the pulse laser light emitted from thelaser light source; calculating means for calculating data of a secondrelative movement amount of the object to be processed in the thicknessdirection required for locating the light-converging point of the pulselaser light converged by the light-converging means at the entranceface; and second moving means for relatively moving the object to beprocessed in the thickness direction according to the data of firstrelative movement amount stored by the storage means and the data ofsecond relative movement amount calculated by the calculating means.

The laser processing apparatus in accordance with an aspect of thepresent invention comprises a laser light source for emitting pulselaser light having a pulse width of 1 μs or less; light-converging meansfor converging the pulse laser light emitted from the laser light sourcesuch that the pulse laser light attains a peak power density of at least1×10⁸ (W/cm²) at a light-converging point; means for locating thelight-converging point of the pulse laser light emitted from the laserlight source within an object to be processed; means for adjusting theposition of the pulse laser light converged by the light-convergingmeans within the thickness of the object to be processed; and movingmeans for relatively moving the light-converging point of pulse laserlight along a line along which the object is intended to be cut in theobject to be processed.

For the same reason as that in the laser processing methods inaccordance with the above-mentioned aspects of the present invention,the laser processing apparatus in accordance with these aspects of thepresent invention enable laser processing without generating melt orunnecessary fractures deviating from the line along which the object isintended to be cut in the surface of the object to be processed, andlaser processing in which the position of the light-converging point ofpulse laser light is regulated in the thickness direction of the objectto be processed within the object.

The present invention will be more fully understood from the detaileddescription given hereinbelow and the accompanying drawings, which aregiven by way of illustration only and are not to be considered aslimiting the present invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificembodiments, while indicating preferred embodiments of the invention,are given by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will beapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an object to be processed during laserprocessing by the laser processing method in accordance with anembodiment;

FIG. 2 is a sectional view of the object to be processed shown in FIG. 1taken along the line II-II;

FIG. 3 is a plan view of the object to be processed after laserprocessing effected by the laser processing method in accordance withthe embodiment;

FIG. 4 is a sectional view of the object to be processed shown in FIG. 3taken along the line IV-IV;

FIG. 5 is a sectional view of the object to be processed shown in FIG. 3taken along the line V-V;

FIG. 6 is a plan view of the object to be processed cut by the laserprocessing method in accordance with the embodiment;

FIG. 7 is a graph showing relationships between the electric fieldintensity and the magnitude of crack in the laser processing method inaccordance with the embodiment;

FIG. 8 is a sectional view of the object to be processed in a first stepof the laser processing method in accordance with the embodiment;

FIG. 9 is a sectional view of the object to be processed in a secondstep of the laser processing method in accordance with the embodiment;

FIG. 10 is a sectional view of the object to be processed in a thirdstep of the laser processing method in accordance with the embodiment;

FIG. 11 is a sectional view of the object to be processed in a fourthstep of the laser processing method in accordance with the embodiment;

FIG. 12 is a view shoring a photograph of a cross section in a part of asilicon wafer cut by the laser processing method in accordance with theembodiment;

FIG. 13 is a graph showing relationships between the laser lightwavelength and the transmittance within a silicon substrate in the laserprocessing method in accordance with the embodiment;

FIG. 14 is a schematic diagram of a laser processing apparatus usable inthe laser processing method in accordance with a first embodiment of theembodiment;

FIG. 15 is a flowchart for explaining the laser processing method inaccordance with the first embodiment of the present invention;

FIG. 16 is a plan view of an object to be processed for explaining apattern which can be cut by the laser processing method in accordancewith the first embodiment of the embodiment;

FIG. 17 is a schematic view for explaining the laser processing methodin accordance with the first embodiment of the embodiment with aplurality of laser light sources;

FIG. 18 is a schematic view for explaining another laser processingmethod in accordance with the first embodiment of the embodiment with aplurality of laser light sources;

FIG. 19 is a schematic plan view showing a piezoelectric device wafer ina state held by a wafer sheet in the second embodiment of theembodiment;

FIG. 20 is a schematic sectional view showing a piezoelectric devicewafer in a state held by the wafer sheet in the second embodiment of theembodiment;

FIG. 21 is a flowchart for explaining the cutting method in accordancewith the second embodiment of the embodiment;

FIG. 22 is a sectional view of a light-transmitting material irradiatedwith laser light by the cutting method in accordance with the secondembodiment of the embodiment;

FIG. 23 is a plan view of the light-transmitting material irradiatedwith laser light by the cutting method in accordance with the secondembodiment of the embodiment;

FIG. 24 is a sectional view of the light-transmitting material shown inFIG. 23 taken along the line XXIV-XXIV;

FIG. 25 is a sectional view of the light-transmitting material shown inFIG. 23 taken along the line XXV-XXV;

FIG. 26 is a sectional view of the light-transmitting material shown inFIG. 23 taken along the line XXV-XXV when the light-converging pointmoving speed is made lower;

FIG. 27 is a sectional view of the light-transmitting material shown inFIG. 23 taken along the line XXV-XXV when the light-converging pointmoving speed is made further lower;

FIG. 28 is a sectional view of a piezoelectric device wafer or the likeshowing a first step of the cutting method in accordance with the secondembodiment of the embodiment;

FIG. 29 is a sectional view of the piezoelectric device wafer or thelike showing a second step of the cutting method in accordance with thesecond embodiment of the embodiment;

FIG. 30 is a sectional view of the piezoelectric device wafer or thelike showing a third step of the cutting method in accordance with thesecond embodiment of the embodiment;

FIG. 31 is a sectional view of the piezoelectric device wafer or thelike showing a fourth step of the cutting method in accordance with thesecond embodiment of the embodiment;

FIG. 32 is a sectional view of the piezoelectric device wafer or thelike showing a fifth step of the cutting method in accordance with thesecond embodiment of the embodiment;

FIG. 33 is a view showing a photograph of a plane of a sample withinwhich a crack region is formed upon irradiation with linearly polarizedpulse laser light;

FIG. 34 is a view showing a photograph of a plane of a sample withinwhich a crack region is formed upon irradiation with circularlypolarized pulse laser light;

FIG. 35 is a sectional view of the sample shown in FIG. 33 taken alongthe line XXXV-XXXV;

FIG. 36 is a sectional view of the sample shown in FIG. 34 taken alongthe line XXXVI-XXXVI;

FIG. 37 is a plan view of the part of object to be processed extendingalong a line along which the object is intended to be cut, in which acrack region is formed by the laser processing method in accordance witha third embodiment of the embodiment;

FIG. 38 is a plan view of the part of object to be processed extendingalong a line along which the object is intended to be cut, in which acrack region is formed by a comparative laser processing method;

FIG. 39 is a view showing elliptically polarized laser light inaccordance with the third embodiment of the embodiment, and a crackregion formed thereby;

FIG. 40 is a schematic diagram of the laser processing apparatus inaccordance with the third embodiment of the embodiment;

FIG. 41 is a perspective view of a quarter-wave plate included in anellipticity regulator in accordance with the third embodiment of theembodiment;

FIG. 42 is a perspective view of a half-wave plate included in a 90°rotation regulator part in accordance with the third embodiment of theembodiment;

FIG. 43 is a flowchart for explaining the laser processing method inaccordance with the third embodiment of the embodiment;

FIG. 44 is a plan view of a silicon wafer irradiated with ellipticallypolarized laser light by the laser processing method in accordance withthe third embodiment of the embodiment;

FIG. 45 is a plan view of a silicon wafer irradiated with linearlypolarized laser light by the laser processing method in accordance withthe third embodiment of the embodiment;

FIG. 46 is a plan view of a silicon wafer in which the silicon wafershown in FIG. 44 is irradiated with elliptically polarized laser lightby the laser processing method in accordance with the third embodimentof the embodiment;

FIG. 47 is a plan view of a silicon wafer in which the silicon wafershown in FIG. 45 is irradiated with linearly polarized laser light bythe laser processing method in accordance with the third embodiment ofthe embodiment;

FIG. 48 is a schematic diagram of the laser processing apparatus inaccordance with a fourth embodiment of the embodiment;

FIG. 49 is a plan view of a silicon wafer in which the silicon wafershown in FIG. 44 is irradiated with elliptically polarized laser lightby the laser processing method in accordance with the fourth embodimentof the embodiment;

FIG. 50 is a plan view of the object to be processed in the case where acrack spot is formed relatively large by using the laser processingmethod in accordance with a fifth embodiment of the embodiment;

FIG. 51 is a sectional view taken along LI-LI on the line along whichthe object is intended to be cut shown in FIG. 50;

FIG. 52 is a sectional view taken along LII-LII orthogonal to the linealong which the object is intended to be cut shown in FIG. 50;

FIG. 53 is a sectional view taken along LIII-LIII orthogonal to the linealong which the object is intended to be cut shown in FIG. 50;

FIG. 54 is a sectional view taken along LIV-LIV orthogonal to the linealong which the object is intended to be cut shown in FIG. 50;

FIG. 55 is a plan view of the object to be processed shown in FIG. 50cut along the line along which the object is intended to be cut;

FIG. 56 is a sectional view of the object to be processed taken alongthe line along which the object is intended to be cut in the case wherea crack spot is formed relatively small by using the laser processingmethod in accordance with the fifth embodiment of the embodiment;

FIG. 57 is a plan view of the object to be processed shown in FIG. 56cut along the line along which the object is intended to be cut;

FIG. 58 is a sectional view of the object to be processed showing astate where pulse laser light is converged within the object by using alight-converging lens having a predetermined numerical aperture;

FIG. 59 is a sectional view of the object to be processed including acrack spot formed due to the multiphoton absorption caused byirradiation with laser light shown in FIG. 58;

FIG. 60 is a sectional view of the object to be processed in the casewhere a light-converging lens having a numerical aperture greater thanthat of the embodiment shown in FIG. 58 is used;

FIG. 61 is a sectional view of the object to be processed including acrack spot formed due to the multiphoton absorption caused byirradiation with laser light shown in FIG. 60;

FIG. 62 is a sectional view of the object to be processed in the casewhere pulse laser light having a power lower than that of the embodimentshown in FIG. 58 is used;

FIG. 63 is a sectional view of the object to be processed including acrack spot formed due to the multiphoton absorption caused byirradiation with laser light shown in FIG. 62;

FIG. 64 is a sectional view of the object to be processed in the casewhere pulse laser light having a power lower than that of the embodimentshown in FIG. 60 is used;

FIG. 65 is a sectional view of the object to be processed including acrack spot formed due to the multiphoton absorption caused byirradiation with laser light shown in FIG. 64;

FIG. 66 is a sectional view taken along LXVI-LXVI orthogonal to the linealong which the object is intended to be cut shown in FIG. 57;

FIG. 67 is a schematic diagram showing the laser processing apparatus inaccordance with the fifth embodiment of the embodiment;

FIG. 68 is a block diagram showing a part of an embodiment of overallcontroller provided in the laser processing apparatus in accordance withthe fifth embodiment of the embodiment;

FIG. 69 is a view showing an embodiment of table of a correlationstoring section included in the overall controller of the laserprocessing apparatus in accordance with the fifth embodiment of theembodiment;

FIG. 70 is a view showing another embodiment of the table of thecorrelation storing section included in the overall controller of thelaser processing apparatus in accordance with the fifth embodiment ofthe embodiment;

FIG. 71 is a view showing still another embodiment of the table of thecorrelation storing section included in the overall controller of thelaser processing apparatus in accordance with the fifth embodiment ofthe embodiment;

FIG. 72 is a schematic diagram of the laser processing apparatus inaccordance with a sixth embodiment of the embodiment;

FIG. 73 is a view showing the convergence of laser light caused by alight-converging lens in the case where no beam expander is disposed;

FIG. 74 is a view showing the convergence of laser light caused by thelight-converging lens in the case where a beam expander is disposed;

FIG. 75 is a schematic diagram of the laser processing apparatus inaccordance with a seventh embodiment of the embodiment;

FIG. 76 is a view showing the convergence of laser light caused by thelight-converging lens in the case where no iris diaphragm is disposed;

FIG. 77 is a view showing the convergence of laser light caused by thelight-converging lens in the case where an iris diaphragm is disposed;

FIG. 78 is a block diagram showing an embodiment of overall controllerprovided in a modified embodiment of the laser processing apparatus inaccordance with the embodiment;

FIG. 79 is a block diagram of another embodiment of overall controllerprovided in the modified embodiment of the laser processing apparatus inaccordance with the embodiment;

FIG. 80 is a block diagram of still another embodiment of overallcontroller provided in the modified embodiment of the laser processingapparatus in accordance with the embodiment;

FIG. 81 is a plan view of an embodiment of the part of object to beprocessed extending along a line along which the object is intended tobe cut, in which a crack region is formed by the laser processing methodin accordance with an eighth embodiment of the embodiment;

FIG. 82 is a plan view of another embodiment of the part of object to beprocessed extending along the line along which the object is intended tobe cut, in which a crack region is formed by the laser processing methodin accordance with the eighth embodiment of the embodiment;

FIG. 83 is a plan view of still another embodiment of the part of objectto be processed extending along the line along which the object isintended to be cut, in which a crack region is formed by the laserprocessing method in accordance with the eighth embodiment of theembodiment;

FIG. 84 is a schematic diagram of a Q-switch laser provided in a laserlight source of the laser processing apparatus in accordance with theeighth embodiment of the embodiment;

FIG. 85 is a block diagram showing a part of an embodiment of overallcontroller of the laser processing apparatus in accordance with theeighth embodiment of the embodiment;

FIG. 86 is a block diagram showing a part of another embodiment ofoverall controller of the laser processing apparatus in accordance withthe eighth embodiment of the embodiment;

FIG. 87 is a block diagram showing a part of still another embodiment ofoverall controller of the laser processing apparatus in accordance withthe eighth embodiment of the embodiment;

FIG. 88 is a block diagram showing a part of still another embodiment ofoverall controller of the laser processing apparatus in accordance withthe eighth embodiment of the embodiment;

FIG. 89 is a perspective view of an embodiment of the object to beprocessed within which a crack region is formed by using the laserprocessing method in accordance with a ninth embodiment of theembodiment;

FIG. 90 is a perspective view of the object to be processed formed witha crack extending from the crack region shown in FIG. 89;

FIG. 91 is a perspective view of another embodiment of the object to beprocessed within which a crack region is formed by using the laserprocessing method in accordance with the ninth embodiment of theembodiment;

FIG. 92 is a perspective view of still another embodiment of the objectto be processed within which a crack region is formed by using the laserprocessing method in accordance with the ninth embodiment of theembodiment;

FIG. 93 is a view showing the state where a light-converging point oflaser light is positioned on the surface of the object to be processed;

FIG. 94 is a view showing the state where a light-converging point oflaser light is positioned within the object to be processed;

FIG. 95 is a flowchart for explaining the laser processing method inaccordance with the ninth embodiment of the embodiment;

FIG. 96 is a perspective view of an embodiment of the object to beprocessed within which a crack region is formed by using the laserprocessing method in accordance with a tenth embodiment of theembodiment;

FIG. 97 is a partly sectional view of the object to be processed shownin FIG. 96;

FIG. 98 is a perspective view of another embodiment of the object to beprocessed within which a crack region is formed by using the laserprocessing method in accordance with the tenth embodiment of theembodiment;

FIG. 99 is a partly sectional view of the object to be processed shownin FIG. 98; and

FIG. 100 is a perspective view of still another embodiment of the objectto be processed within which a crack region is formed by using the laserprocessing method in accordance with the tenth embodiment of theembodiment.

FIG. 101 is a flowchart for explaining the laser processing method inaccordance with the eleventh embodiment of the present invention;

FIG. 102 is a sectional view of the object including a crack regionduring laser processing in the modified region forming step inaccordance with the eleventh and twelfth embodiments.

FIG. 103 is a sectional view of the object including a crack regionduring laser processing in the stress step in accordance with theeleventh embodiment.

FIG. 104 is a flowchart for explaining the laser processing method inaccordance with the twelfth embodiment of the present invention.

FIG. 105 is a sectional view of the object including a crack regionduring laser processing in the stress step in accordance with thetwelfth embodiment.

FIG. 106 shows an film expansion apparatus used in the thirteenthembodiments.

FIG. 107 is for explanation of the expansion status of the adhesive andexpansive sheet in the thirteenth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following, a preferred embodiment of the present invention willbe explained with reference to the drawings. The laser processing methodand laser processing apparatus of an embodiment in accordance with thepresent invention is embodiment form a modified region by multiphotonabsorption. The multiphoton absorption is a phenomenon occurring whenthe intensity of laser light is made very high. First, the multiphotonabsorption will be explained in brief.

A material becomes optically transparent when the energy hν of a photonis lower than the bandgap E_(G) of absorption of the material.Therefore, the condition under which absorption occurs in the materialis hν>E_(G). Even when optically transparent, however, absorption occursin the material under the condition of nhν>E_(G) (n=2, 3, 4, . . . )when the intensity of laser light is made very high. This phenomenon isknown as multiphoton absorption. In the case of pulse wave, theintensity of laser light is determined by the peak power density (W/cm²)of laser light at the light-converging point, whereas the multiphotonabsorption occurs under the condition with a peak power density of atleast 1×10⁸ (W/cm²), for embodiment. The peak power density isdetermined by (energy of laser light at the light-converging point perpulse)/(beam spot cross-sectional area of laser light×pulse width). Inthe case of a continuous wave, the intensity of laser light isdetermined by the electric field intensity (W/cm²) of laser light at thelight-converging point.

The principle of laser processing in accordance with the embodimentutilizing such multiphoton absorption will now be explained withreference to FIGS. 1 to 6. FIG. 1 is a plan view of an object to beprocessed 1 during laser processing. FIG. 2 is a sectional view of theobject 1 shown in FIG. 1 taken along the line II-II. FIG. 3 is a planview of the object 1 after laser processing. FIG. 4 is a sectional viewof the object 1 shown in FIG. 3 taken along the line IV-IV. FIG. 5 is asectional view of the object 1 shown in FIG. 3 taken along the line V-V.FIG. 6 is a plan view of the cut object 1.

As shown in FIGS. 1 and 2, the object 1 has a surface 3 with a line 5along which the object is intended to be cut. The line 5 along which theobject is intended to be cut is a linearly extending virtual line. Inthe laser processing of an embodiment in accordance with the presentinvention, the object 1 is irradiated with laser light L while locatinga light-converging point P within the object 1 under a conditiongenerating multiphoton absorption, so as to form a modified region 7.The light-converging point refers to a location at which the laser lightL is converged.

By relatively moving the laser light L along the line 5 along which theobject is intended to be cut (i.e., along the direction of arrow A), thelight-converging point P is moved along the line 5 along which theobject is intended to be cut. This forms the modified region 7 along theline 5 along which the object is intended to be cut only within theobject 1 as shown in FIGS. 3 to 5. In the laser processing method inaccordance with the embodiment, the modified region 7 is not formed byheating the object 1 due to the absorption of laser light L therein. Thelaser light L is transmitted through the object 1, so as to generatemultiphoton absorption therewithin, thereby forming the modified region7. Therefore, the laser light L is hardly absorbed at the surface 3 ofthe object 1, whereby the surface 3 of the object 1 will not melt.

If a starting point exists in a part to be cut when cutting the object1, the object 1 will break from the starting point, whereby the object 1can be cut with a relatively small force as shown in FIG. 6. Hence, theobject 1 can be cut without generating unnecessary fractures in thesurface 3 of the object 1.

The following two cases seem to exist in the cutting of the object to beprocessed using the modified region as a starting point. The first caseis where, after the modified region is formed, an artificial force isapplied to the object, whereby the object breaks while using themodified region as a starting point, and thus is cut. This is cutting inthe case where the object to be processed has a large thickness, forembodiment. Applying an artificial force includes, for embodiment,applying a bending stress or shearing stress to the object along theline along which the object is intended to be cut in the object to beprocessed or imparting a temperature difference to the object so as togenerate a thermal stress. Another case is where a modified region isformed, so that the object naturally breaks in the cross-sectionaldirection (thickness direction) of the object while using the modifiedregion as a starting point, whereby the object is cut. This can beachieved by a single modified region when the thickness of the object issmall, and by a plurality of modified regions formed in the thicknessdirection when the thickness of the object to be processed is large.Breaking and cutting can be carried out with favorable control even inthis naturally breaking case, since breaks will not reach the partformed with no modified region on the surface in the part to be cut, sothat only the part formed with the modified region can be broken andcut. Such a breaking and cutting method with favorable controllabilityis quite effective, since semiconductor wafers such as silicon wafershave recently been prone to decrease their thickness.

The modified region formed by multiphoton absorption in the embodimentincludes the following (1) to (3):

(1) Case where the Modified Region is a Crack Region Including One or aPlurality of Cracks

An object to be processed (e.g., glass or a piezoelectric material madeof LiTaO₃) is irradiated with laser light while the light-convergingpoint is located therewithin under a condition with a peak power densityof at least 1×10⁸ (W/cm²) and a pulse width of 1 μs or less at thelight-converging point. This magnitude of pulse width is a conditionunder which a crack region can be formed only within the object to beprocessed while generating multiphoton absorption without causingunnecessary damages to the surface of the object. This generates aphenomenon of optical damage caused by multiphoton absorption within theobject to be processed. This optical damage induces thermal distortionwithin the object to be processed, thereby forming a crack regiontherewithin. The upper limit of electric field intensity is 1×10¹²(W/cm²), for embodiment. The pulse width is preferably 1 ns to 200 ns,for embodiment. The forming of a crack region caused by multiphotonabsorption is described, for embodiment, in “Internal Marking of GlassSubstrate by Solid-state Laser Harmonics”, Proceedings of 45th LaserMaterials Processing Conference (December 1998), pp. 23-28.

The inventor determined relationships between the electric fieldintensity and the magnitude of crack by an experiment. Conditions forthe experiment are as follows:

-   -   (A) Object to be processed: Pyrex glass (having a thickness of        700 μm)    -   (B) Laser        -   Light source: semiconductor laser pumping Nd:YAG laser        -   Wavelength: 1064 nm        -   Laser light spot cross-sectional area: 3.14×10⁻⁸ cm²        -   Oscillation mode: Q-switch pulse        -   Repetition frequency: 100 kHz        -   Pulse width: 30 ns        -   Output: output<1 mJ/pulse        -   Laser light quality: TEM₀₀        -   Polarization characteristic: linear polarization    -   (C) Light-converging lens        -   Transmittance with respect to laser light wavelength: 60%    -   (D) Moving speed of a mounting table mounting the object to be        processed: 100 mm/sec

The laser light quality of TEM₀₀ indicates that the light convergence isso high that light can be converged up to about the wavelength of laserlight.

FIG. 7 is a graph showing the results of the above-mentioned experiment.The abscissa indicates peak power density. Since laser light is pulselaser light, its electric field intensity is represented by the peakpower density. The ordinate indicates the size of a crack part (crackspot) formed within the object to be processed by one pulse of laserlight. An assembly of crack spots forms a crack region. The size of acrack spot refers to that of the part of dimensions of the crack spotyielding the maximum length. The data indicated by black circles in thegraph refers to a case where the light-converging glass (C) has amagnification of ×100 and a numerical aperture (NA) of 0.80. On theother hand, the data indicated by white circles in the graph refers to acase where the light-converging glass (C) has a magnification of ×50 anda numerical aperture (NA) of 0.55. It is seen that crack spots begin tooccur within the object to be processed when the peak power densityreaches 10¹¹ (W/cm²), and become greater as the peak power densityincreases.

A mechanism by which the object to be processed is cut upon formation ofa crack region in the laser processing in accordance with the embodimentwill now be explained with reference to FIGS. 8 to 11. As shown in FIG.8, the object to be processed 1 is irradiated with laser light L whilelocating the light-converging point P within the object 1 under acondition where multiphoton absorption occurs, so as to form a crackregion 9 therewithin. The crack region 9 is a region including one or aplurality of cracks. As shown in FIG. 9, the crack further grows whileusing the crack region 9 as a starting point. As shown in FIG. 10, thecrack reaches the surface 3 and rear face 21 of the object 1. As shownin FIG. 11, the object 1 breaks, so as to be cut. The crack reaching thesurface and rear face of the object to be processed may grow naturallyor grow as a force is applied to the object.

(2) Case where the Modified Region is a Molten Processed Region

An object to be processed (e.g., a semiconductor material such assilicon) is irradiated with laser light while the light-converging pointis located therewithin under a condition with a peak power density of atleast 1×10⁸ (W/cm²) and a pulse width of 1 μs or less at thelight-converging point. As a consequence, the inside of the object to beprocessed is locally heated by multiphoton absorption. This heatingforms a molten processed region within the object to be processed. Themolten processed region refers to at least one of a region once meltedand then re-solidified, a region in a melted state, and a region in theprocess of re-solidifying from its melted state. The molten processedregion may also be defined as a phase-changed region or a region havingchanged its crystal structure. The molten processed region may also beregarded as a region in which a certain structure has changed intoanother structure in monocrystal, amorphous, and polycrystal structures.Namely, it refers to a region in which a monocrystal structure haschanged into an amorphous structure, a region in which a monocrystalstructure has changed into a polycrystal structure, and a region inwhich a monocrystal structure has changed into a structure including anamorphous structure and a polycrystal structure, for embodiment. Whenthe object to be processed is a silicon monocrystal structure, themolten processed region is an amorphous silicon structure, forembodiment. The upper limit of electric field intensity is 1×10¹²(W/cm²), for embodiment. The pulse width is preferably 1 ns to 200 ns,for embodiment.

By an experiment, the inventor has verified that a molten processedregion is formed within a silicon wafer. Conditions for the experimentis as follows:

-   -   (A) Object to be processed: silicon wafer (having a thickness of        350 μm and an outer diameter of 4 inches)    -   (B) Laser        -   Light source: semiconductor laser pumping Nd:YAG laser        -   Wavelength: 1064 nm        -   Laser light spot cross-sectional area: 3.14×10⁻⁸ cm²        -   Oscillation mode: Q-switch pulse        -   Repetition frequency: 100 kHz        -   Pulse width: 30 ns        -   Output: 20 μJ/pulse        -   Laser light quality: TEM₀₀        -   Polarization characteristic: linear polarization    -   (C) Light-converging lens        -   Magnification: ×50        -   NA: 0.55        -   Transmittance with respect to laser light wavelength: 60%    -   (D) Moving speed of a mounting table mounting the object to be        processed: 100 mm/sec

FIG. 12 is a view showing a photograph of across section in a part of asilicon wafer cut by laser processing under the above-mentionedconditions. A molten processed region 13 is formed within a siliconwafer 11. The size of the molten processed region formed under theabove-mentioned conditions is about 100 μm in the thickness direction.

The forming of the molten processed region 13 by multiphoton absorptionwill be explained. FIG. 13 is a graph showing relationships between thewavelength of laser light and the transmittance within the siliconsubstrate. Here, respective reflecting components on the surface andrear face sides of the silicon substrate are eliminated, whereby onlythe transmittance therewithin is represented. The above-mentionedrelationships are shown in the cases where the thickness t of thesilicon substrate is 50 μm, 100 μm, 200 μm, 500 μm, and 1000 μm,respectively.

For embodiment, it is seen that laser light transmits through thesilicon substrate by at least 80% at 1064 nm, which is the wavelength ofNd:YAG laser, when the silicon substrate has a thickness of 500 μm orless. Since the silicon wafer 11 shown in FIG. 12 has a thickness of 350μm, the molten processed region caused by multiphoton absorption isformed near the center of the silicon wafer, i.e., at a part separatedfrom the surface by 175 μm. The transmittance in this case is 90% orgreater with reference to a silicon wafer having a thickness of 200 μm,whereby the laser light is absorbed within the silicon wafer 11 onlyslightly and is substantially transmitted therethrough. This means thatthe molten processed region is not formed by laser light absorptionwithin the silicon wafer 11 (i.e., not formed upon usual heating withlaser light), but by multiphoton absorption. The forming of a moltenprocessed region by multiphoton absorption is described, for embodiment,in “Processing Characteristic evaluation of Silicon by Picosecond PulseLaser”, Preprints of the National Meeting of Japan Welding Society, No.66 (April 2000), pp. 72-73.

Here, a fracture is generated in the cross-sectional direction whileusing the molten processed region as a starting point, whereby thesilicon wafer is cut when the fracture reaches the surface and rear faceof the silicon wafer. The fracture reaching the surface and rear face ofthe object to be processed may grow naturally or grow as a force isapplied to the object. The fracture naturally grows from the moltenprocessed region to the surface and rear face of the silicon wafer inone of the cases where the fracture grows from a region once melted andthen re-solidified, where the fracture grows from a region in a meltedstate, and where the fracture grows from a region in the process ofre-solidifying from a melted state. In any of these cases, the moltenprocessed region is formed only within the cross section after cuttingas shown in FIG. 12. When a molten processed region is formed within theobject to be processed, unnecessary fractures deviating from a linealong which the object is intended to be cut are hard to occur at thetime of breaking and cutting, which makes it easier to control thebreaking and cutting.

(3) Case where the Modified Region is a Refractive Index Change Region

An object to be processed (e.g., glass) is irradiated with laser lightwhile the light-converging point is located therewithin under acondition with a peak power density of at least 1×10⁸ (W/cm²) and apulse width of 1 ns or less at the light-converging point. Whenmultiphoton absorption is generated within the object to be processedwith a very short pulse width, the energy caused by multiphotonabsorption is not transformed into thermal energy, so that a permanentstructural change such as ionic valence change, crystallization, orpolarization orientation is induced within the object, whereby arefractive index change region is formed. The upper limit of electricfield intensity is 1×10¹² (W/cm²), for embodiment. The pulse width ispreferably 1 ns or less, more preferably 1 μs or less, for embodiment.The forming of a refractive index change region by multiphotonabsorption is described, for embodiment, in “Formation of PhotoinducedStructure within Glass by Femtosecond Laser Irradiation”, Proceedings of42th Laser Materials Processing Conference (November 1997), pp. 105-111.

Specific embodiments according to the present invention will now beexplained.

First Embodiment

The laser processing method in accordance with a first embodiment of thepresent invention will be explained. FIG. 14 is a schematic diagram of alaser processing apparatus 100 usable in this method. The laserprocessing apparatus 100 comprises a laser light source 101 forgenerating laser light L; a laser light source controller 102 forcontrolling the laser light source 101 so as to regulate the output andpulse width of laser light L and the like; a dichroic mirror 103,arranged so as to change the orientation of the optical axis of laserlight L by 90°, having a function of reflecting the laser light L; alight-converging lens 105 for converging the laser light L reflected bythe dichroic mirror 103; a mounting table 107 for mounting an object tobe processed 1 irradiated with the laser light L converged by thelight-converging lens 105; an X-axis stage 109 for moving the mountingtable 107 in the X-axis direction; a Y-axis stage 111 for moving themounting table 107 in the Y-axis direction orthogonal to the X-axisdirection; a Z-axis stage 113 for moving the mounting table 107 in theZ-axis direction orthogonal to X- and Y-axis directions; and a stagecontroller 115 for controlling the movement of these three stages 109,111, 113.

The Z-axis direction is a direction orthogonal to the surface 3 of theobject to be processed 1, thus becoming the direction of focal depth oflaser light L incident on the object 1. Therefore, moving the Z-axisstage 113 in the Z-axis direction can locate the light-converging pointP of laser light L within the object 1. This movement oflight-converging point P in X(Y)-axis direction is effected by movingthe object 1 in the X(Y)-axis direction by the X(Y)-axis stage 109(111). The X(Y)-axis stage 109 (111) is an embodiment of moving means.

The laser light source 101 is an Nd:YAG laser generating pulse laserlight. Known as other kinds of laser usable as the laser light source101 include Nd:YVO₄ laser, Nd:YLF laser, and titanium sapphire laser.For forming a crack region or molten processed region, Nd:YAG laser,Nd:YVO₄ laser, and Nd:YLF laser are used preferably. For forming arefractive index change region, titanium sapphire laser is usedpreferably.

Though pulse laser light is used for processing the object 1 in thefirst embodiment, continuous wave laser light may also be used as longas it can generate multiphoton absorption. In the present invention,laser light means to include laser beams. The light-converging lens 105is an embodiment of light-converging means. The Z-axis stage 113 is anembodiment of means for locating the light-converging point within theobject to be processed. The light-converging point of laser light can belocated within the object to be processed by relatively moving thelight-converging lens 105 in the Z-axis direction.

The laser processing apparatus 100 further comprises an observationlight source 117 for generating a visible light beam for irradiating theobject to be processed 1 mounted on the mounting table 107; and avisible light beam splitter 119 disposed on the same optical axis asthat of the dichroic mirror 103 and light-converging lens 105. Thedichroic mirror 103 is disposed between the beam splitter 119 andlight-converging lens 105. The beam splitter 119 has a function ofreflecting about a half of a visual light beam and transmitting theremaining half therethrough, and is arranged so as to change theorientation of the optical axis of the visual light beam by 90°. A halfof the visible light beam generated by the observation light source 117is reflected by the beam splitter 119, and thus reflected visible lightbeam is transmitted through the dichroic mirror 103 and light-converginglens 105, so as to illuminate the surf ace 3 of the object 1 includingthe line 5 along which the object is intended to be cut and the like.

The laser processing apparatus 100 further comprises an image pickupdevice 121 and an imaging lens 123 disposed on the same optical axis asthat of the beam splitter 119, dichroic mirror 103, and light-converginglens 105. An embodiment of the image pickup device 121 is a CCD(charge-coupled device) camera. The reflected light of the visual lightbeam having illuminated the surface 3 including the line 5 along whichthe object is intended to be cut and the like is transmitted through thelight-converging lens 105, dichroic mirror 103, and beam splitter 119and forms an image by way of the imaging lens 123, whereas thus formedimage is captured by the imaging device 121, so as to yield imagingdata.

The laser processing apparatus 100 further comprises an imaging dataprocessor 125 for inputting the imaging data outputted from the imagingdevice 121, an overall controller 127 for controlling the laserprocessing apparatus 100 as a whole, and a monitor 129. According to theimaging data, the imaging data processor 125 calculates foal point datafor locating the focal point of the visible light generated in theobservation light source 117 onto the surface 3. According to the focalpoint data, the stage controller 115 controls the movement of the Z-axisstage 113, so that the focal point of visible light is located on thesurface 3. Hence, the imaging data processor 125 functions as an autofocus unit. Also, according to the imaging data, the imaging dataprocessor 125 calculates image data such as an enlarged image of thesurface 3. The image data is sent to the overall controller 127,subjected to various kinds of processing, and then sent to the monitor129. As a consequence, an enlarged image or the like is displayed on themonitor 129.

Data from the stage controller 115, image data from the imaging dataprocessor 125, and the like are fed into the overall controller 127.According to these data as well, the overall controller 127 regulatesthe laser light source controller 102, observation light source 117, andstage controller 115, thereby controlling the laser processing apparatus100 as a whole. Thus, the overall controller 127 functions as a computerunit.

With reference to FIGS. 14 and 15, the laser processing method inaccordance with a first embodiment of the embodiment will now beexplained. FIG. 15 is a flowchart for explaining this laser processingmethod. The object to be processed 1 is a silicon wafer.

First, alight absorption characteristic of the object 1 is determined bya spectrophotometer or the like which is not depicted. According to theresults of measurement, a laser light source 101 generating laser lightL having a wavelength to which the object 1 is transparent or exhibits alow absorption is chosen (S101). Next, the thickness of the object 1 ismeasured. According to the result of measurement of thickness and therefractive index of the object 1, the amount of movement of the object 1in the Z-axis direction is determined (S103). This is an amount ofmovement of the object 1 in the Z-axis direction with reference to thelight-converging point of laser light L positioned at the surface 3 ofthe object 1 in order for the light-converging point P of laser light Lto be positioned within the object 1. This amount of movement is fedinto the overall controller 127.

The object 1 is mounted on the mounting table 107 of the laserprocessing apparatus 100. Then, visible light is generated from theobservation light source 117, so as to illuminate the object 1 (S105).The illuminated surface 3 of the object 1 including the line 5 alongwhich the object is intended to be cut is captured by the image pickupdevice 121. Thus obtained imaging data is sent to the imaging dataprocessor 125. According to the imaging data, the imaging data processor125 calculates such focal point data that the focal point of visiblelight from the observation light source 117 is positioned at the surface3 (S107).

The focal point data is sent to the stage controller 115. According tothe focal point data, the stage controller 115 moves the Z-axis stage113 in the Z-axis direction (S109). As a consequence, the focal point ofvisible light from the observation light source 117 is positioned at thesurface 3. According to the imaging data, the imaging data processor 125calculates enlarged image data of the surface 3 of the object includingthe line 5 along which the object is intended to be cut. The enlargedimage data is sent to the monitor 129 by way of the overall controller127, whereby an enlarged image of the line 5 along which the object isintended to be cut and its vicinity is displayed on the monitor 129.

Movement amount data determined at step S103 has been fed into theoverall controller 127 beforehand, and is sent to the stage controller115. According to the movement amount data, the stage controller 115causes the Z-axis stage 113 to move the object 1 in the Z-axis directionat a position where the light-converging point P of laser light L islocated within the object 1 (S111).

Next, laser light L is generated from the laser light source 101, so asto irradiate the line 5 along which the object is intended to be cut inthe surface 3 of the object with the laser light L. Since thelight-converging point P of laser light is positioned within the object1, a molten processed region is formed only within the object 1.Subsequently, the X-axis stage 109 and Y-axis stage 111 are moved alongthe line along which the object is intended to be cut, so as to form amolten processed region along the line 5 along which the object isintended to be cut within the object 1 (S113). Then, the object 1 isbent along the line 5 along which the object is intended to be cut, andthus is cut (S115). This divides the object 1 into silicon chips.

Effects of the first embodiment will be explained. Here, the line 5along which the object is intended to be cut is irradiated with thepulse laser light L under a condition causing multiphoton absorptionwhile locating the light-converging point P within the object 1. Then,the X-axis stage 109 and Y-axis stage 111 are moved, so as to move thelight-converging point P along the line 5 along which the object isintended to be cut. As a consequence, a modified region (e.g., crackregion, molten processed region, or refractive index change region) isformed within the object 1 along the line 5 along which the object isintended to be cut. When a certain starting point exists at a part to becut in the object to be processed, the object can be cut by breaking itwith a relatively small force. Therefore, breaking the object 1 alongthe line 5 along which the object is intended to be cut while using amodified region as a starting point can cut the object 1 with arelatively small force. This can cut the object 1 without generatingunnecessary fractures deviating from the line 5 along which the objectis intended to be cut in the surface 3 of the object 1.

Also, in the first embodiment, the object 1 is irradiated with the pulselaser light L at the line 5 along which the object is intended to be cutunder a condition generating multiphoton absorption in the object 1while locating the light-converging point P within the object 1.Therefore, the pulse laser light L is transmitted through the object 1without substantially being absorbed at the surface 3 of the object 1,whereby the surface 3 will not incur damages such as melting due to theforming of a modified region.

As explained in the foregoing, the first embodiment can cut the object 1without generating unnecessary fractures deviating from the line 5 alongwhich the object is intended to be cut and melt in the surface 3 of theobject. Therefore, when the object is a semiconductor wafer, forembodiment, a semiconductor chip can be cut out from the semiconductorwafer without generating unnecessary fractures deviating from the linealong which the object is intended to be cut and melt in thesemiconductor chip. The same holds for objects to be processed whosesurface is formed with electrode patterns, and those whose surface isformed with electronic devices such as piezoelectric wafers and glasssubstrates formed with display devices such as liquid crystals.Therefore, the first embodiment can improve the yield of products (e.g.,semiconductor chips, piezoelectric device chips, and display devicessuch as liquid crystal) prepared by cutting the object to be processed.

Also, since the line 5 along which the object is intended to be cut inthe surface 3 of the object 1 does not melt, the first embodiment candecrease the width of the line 5 along which the object is intended tobe cut (the width being the interval between regions to becomesemiconductor chips in the case of a semiconductor wafer, forembodiment). This increases the number of products prepared from asingle object to be processed 1, whereby the productivity of productscan be improved.

Since laser light is used for cutting the object 1, the first embodimentenables processing more complicated than that obtained by dicing with adiamond cutter. For embodiment, even when the line 5 along which theobject is intended to be cut has a complicated form as shown in FIG. 16,the first embodiment allows cutting. These effects are similarlyobtained in embodiments which will be explained later.

Not only a single laser light source but also a plurality of laser lightsources may be provided. For embodiment, FIG. 17 is a schematic view forexplaining the laser processing method in the first embodiment of theembodiment in which a plurality of laser light sources are provided.Here, the object 1 is irradiated with three laser beams emitted fromrespective laser light sources 15, 17, 19 from different directionswhile the light-converging point P is located within the object 1. Therespective laser beams from the laser light sources 15, 17 are madeincident on the object 1 from the surface 3 thereof. The laser beam fromthe laser light source 19 is made incident on the object 1 from the rearface 21 thereof. Since a plurality of laser light sources are used, thismakes it possible for the light-converging point to have an electricfield intensity with such a magnitude that multiphoton absorptionoccurs, even when laser light is continuous wave laser light having apower lower than that of pulse laser light. For the same reason,multiphoton absorption can be generated even without a light-converginglens. Though the light-converging point P is formed by the three laserlight sources 15, 17, 19, the present invention is not restrictedthereto as long as a plurality of laser light sources exist therein.

FIG. 18 is a schematic view for explaining another laser processingmethod in accordance with the first embodiment of the embodiment inwhich a plurality of laser light sources are provided. This embodimentcomprises three array light source sections 25, 27, 29 each having aplurality of laser light sources 23 aligning along the line 5 alongwhich the object is intended to be cut. Among the array light sourcesections 25, 27, 29, laser beams emitted from laser light sources 23arranged in the same row form a single light-converging point (e.g.,light-converging point P₁). This embodiment can form a plurality oflight-converging points P₁, P₂, . . . along the line 5 along which theobject is intended to be cut, whereby the processing speed can beimproved. Also, in this embodiment, a plurality of rows of modifiedregions can be formed at the same time upon laser-scanning on thesurface 3 in a direction orthogonal to the line 5 along which the objectis intended to be cut.

Second Embodiment

A second embodiment of the present invention will now be explained. Thisembodiment is directed to a cutting method and cutting apparatus for alight-transmitting material. The light-transmitting material is anembodiment of the objects to be processed. In this embodiment, apiezoelectric device wafer (substrate) having a thickness of about 400μm made of LiTaO₃ is used as a light-transmitting material.

The cutting apparatus in accordance with the second embodiment isconstituted by the laser processing apparatus 100 shown in FIG. 14 andthe apparatus shown in FIGS. 19 and 20. The apparatus shown in FIGS. 19and 20 will be explained. The piezoelectric device wafer 31 is held by awafer sheet (film) 33 acting as holding means. In the wafer sheet 33,the face on the side holding the piezoelectric device wafer 31 is madeof an adhesive resin tape or the like, and has an elasticity. The wafersheet 33 is set on a mounting table 107 while being held with a sampleholder 35. As shown in FIG. 19, the piezoelectric device wafer 31includes a number of piezoelectric device chips 37 which will be cut andseparated later. Each piezoelectric device chip 37 has a circuit section39. The circuit section 39 is formed on the surface of the piezoelectricdevice wafer 31 for each piezoelectric device chip 37, whereas apredetermined gap a (about 80 μm) is formed between adjacent circuitsections 39. FIG. 20 shows a state where minute crack regions 9 asmodified parts are formed within the piezoelectric device wafer 31.

Next, with reference to FIG. 21, the method of cutting alight-transmitting material in accordance with the second embodimentwill be explained. First, a light absorption characteristic of thelight-transmitting material (piezoelectric device wafer 31 made ofLiTaO₃ in the second embodiment) to become a material to be cut isdetermined (S201). The light absorption characteristic can be measuredby using a spectrophotometer or the like. Once the light absorptioncharacteristic is determined, a laser light source 101 generating laserlight L having a wavelength to which the material to be cut istransparent or exhibits a low absorption is chosen according to theresult of determination (S203). In the second embodiment, a YAG laser ofpulse wave (PW) type having a fundamental wave wavelength of 1064 nm ischosen. This YAG laser has a pulse repetition frequency of 20 Hz, apulse width of 6 ns, and a pulse energy of 300 μJ. The spot diameter oflaser light L emitted from the YAG laser is about 20 μm.

Next, the thickness of the material to be cut is measured (S205). Oncethe thickness of the material to be cut is measured, the amount ofdisplacement (amount of movement) of the light-converging point of laserlight L from the surface (entrance face for laser light L) of thematerial to be cut in the optical axis direction of laser light L isdetermined so as to position the light-converging point of laser light Lwithin the material to be cut according to the result of measurement(S207). For embodiment, in conformity to the thickness and refractiveindex of the material to be cut, the amount of displacement (amount ofmovement) of the light-converging point of laser light L is set to ½ ofthe thickness of the material to be cut.

As shown in FIG. 22, due to the difference between the refractive indexin the atmosphere (e.g., air) surrounding the material to be cut and therefractive index of the material to be cut, the actual position of thelight-converging point P of laser light is located deeper than theposition of the light-converging point Q of laser light L converged bythe light-converging lens 105 from the surface of the material to be cut(piezoelectric device wafer 31). Namely, the relationship of “amount ofmovement of Z-axis stage 113 in the optical axis direction of laserlight L×refractive index of the material to be cut=actual amount ofmovement of light-converging point of laser light L” holds in the air.The amount of displacement (amount of movement) of the light-convergingpoint of laser light L is set in view of the above-mentionedrelationship (between the thickness and refractive index of the materialto be cut). Thereafter, the material to be cut held by the wafer sheet33 is mounted on the mounting table 107 placed on the X-Y-Z-axis stage(constituted by the X-axis stage 109, Y-axis stage 111, and Z-axis stage113 in this embodiment) (S209). After the mounting of the material to becut is completed, light is emitted from the observation light source117, so as to irradiate the material to be cut with thus emitted light.Then, according to the result of imaging at the image pickup device 121,focus adjustment is carried out by moving the Z-axis stage 113 so as toposition the light-converging point of laser light L onto the surface ofthe material to be cut (S211). Here, the surface observation image ofpiezoelectric device wafer 31 obtained by the observation light source117 is captured by the image pickup device 121, whereas the imaging dataprocessor 125 determines the moving position of the Z-axis stage 113according to the result of imaging such that the light emitted from theobservation light source 117 forms a focal point on the surface of thematerial to be cut, and outputs thus determined position to the stagecontroller 115. According to an output signal from the imaging dataprocessor 125, the stage controller 115 controls the Z-axis stage 113such that the moving position of the Z-axis stage 113 is located at aposition for making the light emitted from the observation light source117 form a focal point on the material to be cut, i.e., for positioningthe focal point of laser light L onto the surface of the material to becut.

After the focus adjustment of light emitted from the observation lightsource 117 is completed, the light-converging point of laser light L ismoved to a light-converging point corresponding to the thickness andrefractive index of the material to be cut (S213). Here, the overallcontroller 127 sends an output signal to the stage controller 115 so asto move the Z-axis stage 113 in the optical axis direction of laserlight L by the amount of displacement of the light-converging point oflaser light determined in conformity to the thickness and refractiveindex of the material to be cut, whereby the stage controller 115 havingreceived the output signal regulates the moving position of the Z-axisstage 113. As mentioned above, the placement of the light-convergingpoint of laser light L within the material to be cut is completed bymoving the Z-axis stage 113 in the optical axis direction of laser lightL by the amount of displacement of the light-converging point of laserlight L determined in conformity to the thickness and refractive indexof the material to be cut (S215).

After the placement of the light-converging point of laser light Lwithin the material to be cut is completed, the material to be cut isirradiated with laser light L, and the X-axis stage 109 and the Y-axisstage 111 are moved inconformity to a desirable cutting pattern (S217).As shown in FIG. 22, the laser light L emitted from the laser lightsource 101 is converged by the light-converging lens 105 such that thelight-converging point P is positioned within the piezoelectric devicewafer 31 facing a predetermined gap (80 μm as mentioned above) formedbetween adjacent circuit sections 39. The above-mentioned desirablecutting pattern is set such that the gap formed between the adjacentcircuit sections 39 in order to separate a plurality of piezoelectricdevice chips 37 from the piezoelectric device wafer 31 is irradiatedwith the laser light L, whereas the laser light L is irradiated whilethe state of irradiation of laser light L is seen through the monitor129.

Here, as shown in FIG. 22, the laser light L irradiating the material tobe cut is converged by the light-converging lens 105 by an angle atwhich the circuit sections 39 formed on the surface of the piezoelectricdevice wafer 31 (the surface on which the laser light L is incident) arenot irradiated with the laser light L. Converging the laser light L byan angle at which the circuit sections 39 are not irradiated with thelaser light L can prevent the laser light L from entering the circuitsections 39 and protect the circuit sections 39 against the laser lightL.

When the laser light L emitted from the laser light source 101 isconverged such that the light-converging point P is positioned withinthe piezoelectric device wafer 31 while the energy density of laserlight L at the light-converging point P exceeds a threshold of opticaldamage or optical dielectric breakdown, minute crack regions 9 areformed only at the light-converging point P within the piezoelectricdevice wafer 31 acting as a material to be cut and its vicinity. Here,the surface and rear face of the material to be cut (piezoelectricdevice wafer 31) will not be damaged.

Now, with reference to FIGS. 23 to 27, the forming of cracks by movingthe light-converging point of laser light L will be explained. Thematerial to be cut 32 (light-transmitting material) having asubstantially rectangular parallelepiped form shown in FIG. 23 isirradiated with laser light L such that the light-converging point oflaser light L is positioned within the material to be cut 32, wherebyminute crack regions 9 are formed only at the light-converging pointwithin the material to be cut 32 and its vicinity as shown in FIGS. 24and 25. The scanning of laser light L or movement of the material to becut 32 is regulated so as to move the light-converging point of laserlight L in the longitudinal direction D of material to be cut 32intersecting the optical axis of laser light L.

Since the laser light L is emitted from the laser light source 101 in apulsating manner, a plurality of crack regions 9 are formed with a gaptherebetween corresponding to the scanning speed of laser light L or themoving speed of the material to be cut 32 along the longitudinaldirection D of the material to be cut 32 when the laser light L isscanned or the material to be cut 32 is moved. The scanning speed oflaser light L or the moving speed of material to be cut 32 may be sloweddown, so as to shorten the gap between the crack regions 9, therebyincreasing the number of thus formed crack regions 9 as shown in FIG.26. The scanning speed of laser light L or the moving speed of materialto be cut may further be slowed down, so that the crack region 9 iscontinuously formed in the scanning direction of laser light L or themoving direction of material to be cut 32, i.e., the moving direction ofthe light-converging point of laser light L as shown in FIG. 27.Adjustment of the gap between the crack regions 9 (number of crackregions 9 to be formed) can also be realized by changing therelationship between the repetition frequency of laser light L and themoving speed of the material to be cut 32 (X-axis stage or Y-axisstage). Also, throughput can be improved when the repetition frequencyof laser light L and the moving speed of material to be cut 32 areincreased.

Once the crack regions 9 are formed along the above-mentioned desirablecutting pattern (S219), a stress is generated due to physical externalforce application, environmental changes, and the like within thematerial to be cut, the part formed with the crack regions 9 inparticular, so as to grow the crack regions 9 formed only within thematerial to be cut (the light-converging point and its vicinity),thereby cutting the material to be cut at a position formed with thecrack regions 9 (S221).

With reference to FIGS. 28 to 32, the cutting of the material to be cutupon physical external force application will be explained. First, thematerial to be cut (piezoelectric device wafer 31) formed with the crackregions 9 along the desirable cutting pattern is placed in a cuttingapparatus while in a state held by a wafer sheet 33 grasped by thesample holder 35. The cutting apparatus has a suction chuck 34, whichwill be explained later, a suction pump (not depicted) connected to thesuction chuck 34, a pressure needle 36 (pressing member), pressureneedle driving means (not depicted) for moving the pressure needle 36,and the like. Usable as the pressure needle driving means is an actuatorof electric, hydraulic, or other types. FIGS. 28 to 32 do not depict thecircuit sections 39.

Once the piezoelectric device wafer 31 is placed in the cuttingapparatus, the suction chuck 34 approaches the position corresponding tothe piezoelectric device chip 37 to be isolated as shown in FIG. 28. Asuction pump apparatus is actuated while in a state where the suctionchuck 34 is located closer to or abuts against the piezoelectric devicechip 37 to be isolated, whereby the suction chuck 34 attracts thepiezoelectric device chip 37 (piezoelectric device wafer 31) to beisolated as shown in FIG. 29. Once the suction chuck 34 attracts thepiezoelectric device chip 37 (piezoelectric device wafer 31) to beisolated, the pressure needle 36 is moved to the position correspondingto the piezoelectric device chip 37 to be isolated from the rear face ofwafer sheet 33 (rear face of the surface held with the piezoelectricdevice wafer 31) as shown in FIG. 30.

When the pressure needle 36 is further moved after abutting against therear face of the wafer sheet 33, the wafer sheet 33 deforms, while thepressure needle 36 applies a stress to the piezo electric device wafer31 from the outside, whereby a stress is generated in the wafer partformed with the crack regions 9, which grows the crack regions 9. Whenthe crack regions 9 grow to the surface and rear face of thepiezoelectric device wafer 31, the piezoelectric device wafer 31 is cutat an end part of the piezoelectric device chip 37 to be isolated asshown in FIG. 31, whereby the piezoelectric device chip 37 is isolatedfrom the piezoelectric device wafer 31. The wafer sheet 33 has anadhesiveness as mentioned above, thereby being able to prevent cut andseparated piezoelectric device chips 37 from flying away.

Once the piezoelectric device chip 37 is separated from thepiezoelectric device wafer 31, the suction chuck 34 and pressure needle36 are moved away from the wafer sheet 33. When the suction chuck 34 andpressure needle 36 are moved, the isolated piezoelectric device chip 37is released from the wafer sheet 33 as shown in FIG. 32, since theformer is attracted to the suction chuck 34. Here, an ion air blowapparatus, which is not depicted, is used for sending an ion air in thedirection of arrows B in FIG. 32, whereby the piezoelectric device chip37 isolated and attracted to the suction chuck 34, and the piezoelectricdevice wafer 31 (surface) held by the wafer sheet 32 are cleaned withthe ion air. Here, a suction apparatus may be provided in place of theion air cleaning, such that the cut and separated piezoelectric devicechips 37 and piezoelectric device wafer 31 are cleaned as dust and thelike are aspirated. Known as a method of cutting the material to be cutdue to environmental changes is one imparting a temperature change tothe material to be cut having the crack regions 9 only therewithin. Whena temperature change is imparted to the material to be cut as such, athermal distortion can occur in the material part formed with the crackregions 9, so that the crack regions grow, whereby the material to becut can be cut.

Thus, in the second embodiment, the light-converging lens 105 convergesthe laser light L emitted from the laser light source 101 such that itslight-converging point is positioned within the light-transmittingmaterial (piezoelectric device wafer 31), whereby the energy density oflaser light at the light-converging point exceeds the threshold ofoptical damage or optical dielectric breakdown, which forms the minutecracks 9 only at the light-converging point within thelight-transmitting material and its vicinity. Since thelight-transmitting material is cut at the positions of thus formed crackregions 9, the amount of dust emission is very small, whereby thepossibility of dicing damages, chipping, cracks on the material surface,and the like occurring also becomes very low. Since thelight-transmitting material is cut along the crack regions 9 formed bythe optical damages or optical dielectric breakdown of thelight-transmitting material, the directional stability of cuttingimproves, so that cutting direction can be controlled easily. Also, thedicing width can be made smaller than that attained in the dicing with adiamond cutter, whereby the number of light-transmitting materials cutout from one light-transmitting material can be increased. As a resultof these, the second embodiment can cut the light-transmitting materialquite easily and appropriately.

Also, a stress is generated within the material to be cut due tophysical external force application, environmental changes, and thelike, so as to grow the formed crack regions 9 to cut thelight-transmitting material (piezoelectric device wafer 31), whereby thelight-transmitting material can reliably be cut at the positions offormed crack regions 9.

Also, the pressure needle 36 is used for applying a stress to thelight-transmitting material (piezoelectric device wafer 31), so as togrow the formed crack regions 9 to cut the light-transmitting material(piezoelectric device wafer 31), whereby the light-transmitting materialcan further reliably be cut at the positions of formed crack regions 9.

When the piezoelectric device wafer 31 (light-transmitting material)formed with a plurality of circuit sections 39 is cut and separated intoindividual piezoelectric device chips 37, the light-converging lens 105converges the laser light L such that the light-converging point ispositioned within the wafer part facing the gap formed between adjacentcircuit sections 39, and forms the crack regions 9, whereby thepiezoelectric device wafer 31 can reliably be cut at the position of thegap formed between adjacent circuit sections 39.

When the light-transmitting material (piezoelectric device wafer 31) ismoved or laser light L is scanned so as to move the light-convergingpoint in a direction intersecting the optical axis of laser light L,e.g., a direction orthogonal thereto, the crack region 9 is continuouslyformed along the moving direction of the light-converging point, so thatthe directional stability of cutting further improves, which makes itpossible to control the cutting direction more easily.

Also, in the second embodiment, dust-emitting powders hardly exist, sothat no lubricating/cleaning water for preventing the dust-emittingpowders from flying away is necessary, whereby dry processing can berealized in the cutting step.

In the second embodiment, since the forming of a modified part (crackregion 9) is realized by non-contact processing with the laser light L,problems of durability of blades, their replacement frequency, and thelike in the dicing caused by diamond cutters will not occur. Also, sincethe forming of a modified part (crack region 9) is realized bynon-contact processing with the laser light L, the second embodiment cancut the light-transmitting material along a cutting pattern which cutsout the light-transmitting material without completely cutting the same.The present invention is not limited to the above-mentioned secondembodiment. For embodiment, the light-transmitting material may be asemiconductor wafer, a glass substrate, or the like without beingrestricted to the piezoelectric device wafer 31. Also, the laser lightsource 101 can appropriately be selected in conformity to an opticalabsorption characteristic of the light-transmitting material to be cut.Though the minute regions 9 are formed as a modified part uponirradiation with the laser light L in the second embodiment, it is notrestrictive. For embodiment, using an ultra short pulse laser lightsource (e.g., femto second (fs) laser) can form a modified part causedby a refractive index change (higher refractive index), thus being ableto cut the light-transmitting material without generating the crackregions 9 by utilizing such a mechanical characteristic change.

Though the focus adjustment of laser light L is carried out by movingthe Z-axis stage 113 in the laser processing apparatus 100, it may beeffected by moving the light-converging lens 105 in the optical axisdirection of laser light L without being restricted thereto.

Though the X-axis stage 109 and Y-axis stage 111 are moved in conformityto a desirable cutting pattern in the laser processing apparatus 100, itis not restrictive, whereby the laser light L may be scanned inconformity to a desirable cutting pattern.

Though the piezoelectric device wafer 31 is cut by the pressure needle36 after being attracted to the suction chuck 34, it is not restrictive,whereby the piezoelectric device wafer 31 may be cut by the pressureneedle 36, and then the cut and isolated piezoelectric device chip 37may be attracted to the suction chuck 34. Here, when the piezoelectricdevice wafer 31 is cut by the pressure needle 36 after the piezoelectricdevice wafer 31 is attracted to the suction chuck 34, the surface of thecut and isolated piezoelectric device chip 37 is covered with thesuction chuck 34, which can prevent dust and the like from adhering tothe surface of the piezoelectric device chip 37.

Also, when an image pickup device 121 for infrared rays is used, focusadjustment can be carried out by utilizing reflected light of laserlight L. In this case, it is necessary that a half mirror be usedinstead of the dichroic mirror 103, while disposing an optical devicebetween the half mirror and the laser light source 101, which suppressesthe return light to the laser light source 101. Here, it is preferredthat the output of laser light L emitted from the laser light source 101at the time of focus adjustment be set to an energy level lower thanthat of the output for forming cracks, such that the laser light L forcarrying out focus adjustment does not damage the material to be cut.

Characteristic features of the present invention will now be explainedfrom the viewpoints of the second embodiment.

The method of cutting a light-transmitting material in accordance withan aspect of the present invention comprises a modified part formingstep of converging laser light emitted from a laser light source suchthat its light-converging point is positioned within thelight-transmitting material, so as to form a modified part only at thelight-converging point within the light-transmitting material and itsvicinity; and a cutting step of cutting the light-transmitting materialat the position of thus formed modified part.

In the method of cutting a light-transmitting material in accordancewith this aspect of the present invention, the laser light is convergedsuch that the light-converging point of laser light is positioned withinthe light-transmitting material in the modified part forming step,whereby the modified part is formed only at the light-converging pointwithin the light-transmitting material and its vicinity. In the cuttingstep, the light-transmitting material is cut at the position of thusformed modified part, so that the amount of dust emission is very small,whereby the possibility of dicing damages, chipping, cracks on thematerial surface, and the like occurring also becomes very low. Sincethe light-transmitting material is cut at the position of thus formedmodified part, the directional stability of cutting improves, so thatcutting direction can be controlled easily. Also, the dicing width canbe made smaller than that attained in the dicing with a diamond cutter,whereby the number of light-transmitting materials cut out from onelight-transmitting material can be increased. As a result of these, thepresent invention can cut the light-transmitting material quite easilyand appropriately.

Also, in the method of cutting a light-transmitting material inaccordance with this aspect of the present invention, dust-emittingpowders hardly exist, so that no lubricating/cleaning water forpreventing the dust-emitting powders from flying away is necessary,whereby dry processing can be realized in the cutting step.

In the method of cutting a light-transmitting material in accordancewith this aspect of the present invention, since the forming of amodified part is realized by non-contact processing with laser light,problems of durability of blades, their replacement frequency, and thelike in the dicing caused by diamond cutters will not occur. Also, sincethe forming of a modified part is realized by non-contact processingwith the laser light, the method of cutting a light-transmittingmaterial in accordance with this aspect of the present invention can cutthe light-transmitting material along a cutting pattern which cuts outthe light-transmitting material without completely cutting the same.

Preferably, the light-transmitting material is formed with a pluralityof circuit sections, whereas laser light is converged such that thelight-converging point is positioned within the light-transmittingmaterial part facing the gap formed between adjacent circuit sections inthe modified part forming step, so as to form the modified part. Withsuch a configuration, the light-transmitting material can reliably becut at the position of the gap formed between adjacent circuit sections.

When irradiating the light-transmitting material with laser light in themodified part forming step, it is preferred that the laser light beconverged by an angle at which the circuit sections are not irradiatedwith the laser light. Converging the laser light by an angle at whichthe circuit sections are not irradiated with the laser light whenirradiating the light-transmitting material with the laser light in themodified part forming step as such can prevent the laser light fromentering the circuit sections and protect the circuit sections againstthe laser light.

Preferably, in the modified part forming step, the light-convergingpoint is moved in a direction intersecting the optical axis of laserlight, so as to form a modified part continuously along the movingdirection of the light-converging point. When the light-converging pointis moved in a direction intersecting the optical axis of laser light inthe modified part forming step as such, so as to form the modified partcontinuously along the moving direction of the light-converging point,the directional stability of cutting further improves, which makes itfurther easier to control the cutting direction.

The method of cutting a light-transmitting material in accordance withan aspect of the present invention comprises a crack forming step ofconverging laser light emitted from a laser light source such that itslight-converging point is positioned within the light-transmittingmaterial, so as to form a crack only at the light-converging pointwithin the light-transmitting material and its vicinity; and a cuttingstep of cutting the light-transmitting material at the position of thusformed crack.

In the method of cutting a light-transmitting material in accordancewith this aspect of the present invention, laser light is converged suchthat the light-converging point of laser light is positioned within thelight-transmitting material, so that the energy density of laser lightat the light-converging point exceeds a threshold of optical damage oroptical dielectric breakdown of the light-transmitting material, wherebya crack is formed only at the light-converging point within thelight-transmitting material and its vicinity. In the cutting step, thelight-transmitting material is cut at the position of thus formed crack,so that the amount of dust emission is very small, whereby thepossibility of dicing damages, chipping, cracks on the material surface,and the like occurring also becomes very low. Since thelight-transmitting material is cut at the position of the crack formedby an optical damage or optical dielectric breakdown, the directionalstability of cutting improves, so that cutting direction can becontrolled easily. Also, the dicing width can be made smaller than thatattained in the dicing with a diamond cutter, whereby the number oflight-transmitting materials cut out from one light-transmittingmaterial can be increased. As a result of these, the present inventioncan cut the light-transmitting material quite easily and appropriately.

Also, in the method of cutting a light-transmitting material inaccordance with this aspect of the present invention, dust-emittingpowders hardly exist, so that no lubricating/cleaning water forpreventing the dust-emitting powders from flying away is necessary,whereby dry processing can be realized in the cutting step.

In the method of cutting a light-transmitting material in accordancewith this aspect of the present invention, since the forming of a crackis realized by non-contact processing with laser light, problems ofdurability of blades, their replacement frequency, and the like in thedicing caused by diamond cutters will not occur. Also, since the formingof a crack is realized by non-contact processing with the laser light,the method of cutting a light-transmitting material in accordance withthis aspect of the present invention can cut the light-transmittingmaterial along a cutting pattern which cuts out the light-transmittingmaterial without completely cutting the same.

Preferably, in the cutting step, the light-transmitting material is cutby growing the formed crack. Cutting the light-transmitting material bygrowing the formed crack in the cutting step as such can reliably cutthe light-transmitting material at the position of the formed crack.

Preferably, in the cutting step, a stress is applied to thelight-transmitting material by using a pressing member, so as to grow acrack, thereby cutting the light-transmitting material. When a stress isapplied to the light-transmitting material in the cutting step by usinga pressing member as such, so as to grow a crack, thereby cutting thelight-transmitting material, the light-transmitting material can furtherreliably be cut at the position of the crack.

The apparatus for cutting a light-transmitting material in accordancewith an aspect of the present invention comprises a laser light source;holding means for holding the light-transmitting material; an opticaldevice for converging the laser light emitted from the laser lightsource such that a light-converging point thereof is positioned withinthe light-transmitting material; and cutting means for cutting thelight-transmitting material at the position of a modified part formedonly at the light-converging point of laser light within thelight-transmitting material and its vicinity.

In the apparatus for cutting a light-transmitting material in accordancewith this aspect of the present invention, the optical device convergeslaser light such that the light-converging point of laser light ispositioned within the light-transmitting material, whereby a modifiedpart is formed only at the light-converging point within thelight-transmitting material and its vicinity. Then, the cutting meanscuts the light-transmitting material at the position of the modifiedpart formed only at the light-converging point within thelight-transmitting material and its vicinity, whereby thelight-transmitting material is reliably cut along thus formed modifiedpart. As a consequence, the amount of dust emission is very small,whereas the possibility of dicing damages, chipping, cracks on thematerial surface, and the like occurring also becomes very low. Also,since the light-transmitting material is cut along the modified part,the directional stability of cutting improves, whereby the cuttingdirection can be controlled easily. Also, the dicing width can be madesmaller than that attained in the dicing with a diamond cutter, wherebythe number of light-transmitting materials cut out from onelight-transmitting material can be increased. As a result of these, thepresent invention can cut the light-transmitting material quite easilyand appropriately.

Also, in the apparatus for cutting a light-transmitting material inaccordance with this aspect of the present invention, dust-emittingpowders hardly exist, so that no lubricating/cleaning water forpreventing the dust-emitting powders from flying away is necessary,whereby dry processing can be realized in the cutting step.

In the apparatus for cutting a light-transmitting material in accordancewith this aspect of the present invention, since the modified part isformed by non-contact processing with laser light, problems ofdurability of blades, their replacement frequency, and the like in thedicing caused by diamond cutters will not occur as in the conventionaltechniques. Also, since the modified part is formed by non-contactprocessing with the laser light as mentioned above, the apparatus forcutting a light-transmitting material in accordance with this aspect ofthe present invention can cut the light-transmitting material along acutting pattern which cuts out the light-transmitting material withoutcompletely cutting the same.

The apparatus for cutting a light-transmitting material in accordancewith an aspect of the present invention comprises a laser light source;holding means for holding the light-transmitting material; an opticaldevice for converging laser light emitted from the laser light sourcesuch that a light-converging point thereof is positioned within thelight-transmitting material; and cutting means for cutting thelight-transmitting material by growing a crack formed only at thelight-converging point of laser light within the light-transmittingmaterial and its vicinity.

In the apparatus for cutting a light-transmitting material in accordancewith this aspect of the present invention, the optical device convergeslaser light such that the light-converging point of laser light ispositioned within the light-transmitting material, so that the energydensity of laser light at the light-converging point exceeds a thresholdof optical damage or optical dielectric breakdown of thelight-transmitting material, whereby a crack is formed only at thelight-converging point within the light-transmitting material and itsvicinity. Then, the cutting means cuts the light-transmitting materialby growing the crack formed only at the light-converging point withinthe light-transmitting material and its vicinity, whereby thelight-transmitting material is reliably cut along the crack formed by anoptical damage or optical dielectric breakdown of the light-transmittingmaterial. As a consequence, the amount of dust emission is very small,whereas the possibility of dicing damages, chipping, cracks on thematerial surface, and the like occurring also becomes very low. Sincethe light-transmitting material is cut along the crack, the directionalstability of cutting improves, so that cutting direction can becontrolled easily. Also, the dicing width can be made smaller than thatattained in the dicing with a diamond cutter, whereby the number oflight-transmitting materials cut out from one light-transmittingmaterial can be increased. As a result of these, the present inventioncan cut the light-transmitting material quite easily and appropriately.

Also, in the apparatus for cutting a light-transmitting material inaccordance with this aspect of the present invention, dust-emittingpowders hardly exist, so that no lubricating/cleaning water forpreventing the dust-emitting powders from flying away is necessary,whereby dry processing can be realized in the cutting step.

In the apparatus for cutting a light-transmitting material in accordancewith this aspect of the present invention, since the crack is formed bynon-contact processing with laser light, problems of durability ofblades, their replacement frequency, and the like in the dicing causedby diamond cutters will not occur as in the conventional techniques.Also, since the crack is formed by non-contact processing with the laserlight as mentioned above, the method of cutting a light-transmittingmaterial in accordance with this aspect of the present invention can cutthe light-transmitting material along a cutting pattern which cuts outthe light-transmitting material without completely cutting the same.

Preferably, the cutting means has a pressing member for applying astress to the light-transmitting material. When the cutting means has apressing member for applying a stress to the light-transmitting materialas such, a stress can be applied to the light-transmitting material byusing the pressing member, so as to grow a crack, whereby thelight-transmitting material can further reliably be cut at the positionof the crack formed.

Preferably, the light-transmitting material is one whose surface isformed with a plurality of circuit sections, whereas the optical deviceconverges the laser light such that the light-converging point ispositioned within the light-transmitting material part facing the gapformed between adjacent circuit sections. With such a configuration, thelight-transmitting material can reliably be cut at the position of thegap formed between adjacent circuit sections.

Preferably, the optical device converges laser light by an angle atwhich the circuit sections are not irradiated with the laser light. Whenthe optical device converges the laser light by an angle at which thecircuit sections are not irradiated with the laser light as such, it canprevent the laser light from entering the circuit sections and protectthe circuit sections against the laser light.

Preferably, the apparatus further comprises light-converging pointmoving means for moving the light-converging point in a directionintersecting the optical axis of laser light. When the apparatus furthercomprises light-converging point moving means for moving thelight-converging point in a direction intersecting the optical axis oflaser light as such, a crack can continuously be formed along the movingdirection of the light-converging point, so that the directionalstability of cutting further improves, whereby the direction of cuttingcan be controlled further easily.

Third Embodiment

A third embodiment of the present invention will be explained. In thethird embodiment and a fourth embodiment which will be explained later,an object to be processed is irradiated with laser light such that thedirection of linear polarization of linearly polarized laser lightextends along a line along which the object is intended to be cut in theobject to be processed, whereby a modified region is formed in theobject to be processed. As a consequence, in the modified spot formedwith a single pulse of shot (i.e., a single pulse of laser irradiation),the size in the direction extending along the line along which theobject is intended to be cut can be made relatively large when the laserlight is pulse laser light. The inventor has confirmed it by anexperiment. Conditions for the experiment are as follows:

-   -   (A) Object to be processed: Pyrex glass wafer (having a        thickness of 700 μm and an outer diameter of 4 inches)    -   (B) Laser        -   Light source: semiconductor laser pumping Nd:YAG laser        -   Wavelength: 1064 nm        -   Laser light spot cross-sectional area: 3.14×10⁻⁸ cm²        -   Oscillation mode: Q-switch pulse        -   Repetition frequency: 100 kHz        -   Pulse width: 30 ns        -   Output: output<1 mJ/pulse        -   Laser light quality: TEM₀₀        -   Polarization characteristic: linear polarization    -   (C) Light-converging lens        -   Magnification: ×50        -   NA: 0.55        -   Transmittance with respect to laser light wavelength: 60%    -   (D) Moving speed of a mounting table mounting the object to be        processed: 100 mm/sec

Each of Samples 1, 2, which was an object to be processed, was exposedto a single pulse shot of pulse laser light while the light-convergingpoint is located within the object to be processed, whereby a crackregion caused by multiphoton absorption is formed within the object tobe processed. Sample 1 was irradiated with linearly polarized pulselaser light, whereas Sample 2 was irradiated with circularly polarizedpulse laser light.

FIG. 33 is a view showing a photograph of Sample 1 in plan, whereas FIG.34 is a view showing a photograph of Sample 2 in plan. These planes arean entrance face 209 of pulse laser light. Letters LP and CPschematically indicate linear polarization and circular polarization,respectively. FIG. 35 is a view schematically showing a cross section ofSample 1 shown in FIG. 33 taken along the line XXXV-XXXV. FIG. 36 is aview schematically showing a cross section of Sample 1 shown in FIG. 34taken along the line XXXVI-XXXVI. A crack spot 90 is formed within aglass wafer 211 which is the object to be processed.

In the case where pulse laser light is linearly polarized light, asshown in FIG. 35, the size of crack spot 90 formed by a single pulseshot is relatively large in the direction aligning with the direction oflinear polarization. This indicates that the forming of the crack spot90 is accelerated in this direction. When the pulse laser light iscircularly polarized light, by contrast, the size of the crack spot 90formed by a single pulse shot will not become greater in any specificdirection as shown in FIG. 36. The size of the crack spot 90 in thedirection yielding the maximum length is greater in Sample 1 than inSample 2.

The fact that a crack region extending along a line along which theobject is intended to be cut can be formed efficiently will be explainedfrom these results of experiment. FIGS. 37 and 38 are plan views ofcrack regions each formed along a line along which the object isintended to be cut in an object to be processed. A number of crack spots90, each formed by a single pulse shot, are formed along a line 5 alongwhich the object is intended to be cut, whereby a crack region 9extending along the line 5 along which the object is intended to be cutis formed. FIG. 37 shows the crack region 9 formed upon irradiation withpulse laser light such that the direction of linear polarization ofpulse laser light aligns with the line 5 along which the object isintended to be cut. The forming of crack spots 9 is accelerated alongthe direction of the line 5 along which the object is intended to becut, whereby their size is relatively large in this direction.Therefore, the crack region 9 extending along the line 5 along which theobject is intended to be cut can be formed by a smaller number of shots.On the other hand, FIG. 38 shows the crack region 9 formed uponirradiation with pulse laser light such that the direction of linearpolarization of pulse laser light is orthogonal to the line 5 alongwhich the object is intended to be cut. Since the size of crack spot 90in the direction of the line 5 along which the object is intended to becut is relatively small, the number of shots required for forming thecrack region 9 becomes greater than that in the case of FIG. 37.Therefore, the method of forming a crack region in accordance with thisembodiment shown in FIG. 37 can form the crack region more efficientlythan the method shown in FIG. 38 does.

Also, since pulse laser light is irradiated while the direction oflinear polarization of pulse laser light is orthogonal to the line 5along which the object is intended to be cut, the forming of the crackspot 90 formed at the shot is accelerated in the width direction of theline 5 along which the object is intended to be cut. Therefore, when thecrack spot 90 extends in the width direction of the line 5 along whichthe object is intended to be cut too much, the object to be processedcannot precisely be cut along the line 5 along which the object isintended to be cut. By contrast, the crack spot 90 formed at the shotdoes not extend much in directions other than the direction aligningwith the line 5 along which the object is intended to be cut in themethod in accordance with this embodiment shown in FIG. 37, whereby theobject to be processed can be cut precisely.

Though making the size in a predetermined direction relatively largeamong the sizes of a modified region has been explained in the case oflinear polarization, the same holds in elliptical polarization as well.Namely, as shown in FIG. 39, the forming of the crack spot 90 isaccelerated in the direction of major axis b of an ellipse representingelliptical polarization EP of laser light, whereby the crack spot 90having a relatively large size along this direction can be formed.Hence, when a crack region is formed such that the major axis of anellipse indicative of the elliptical polarization of laser ellipticallypolarized with an ellipticity of other than 1 aligns with a line alongwhich the object is intended to be cut in the object to be processed,effects similar to those in the case of linear polarization occur. Here,the ellipticity is half the length of minor axis a/half the length ofmajor axis b. As the ellipticity is smaller, the size of the crack spot90 along the direction of major axis b becomes greater. Linearlypolarized light is elliptically polarized light with an ellipticity ofzero. Circularly polarized light is obtained when the ellipticity is 1,which cannot make the size of the crack region relatively large in apredetermined direction. Therefore, this embodiment does not encompassthe case where the ellipticity is 1.

Though making the size in a predetermined direction relatively largeamong the sizes of a modified region has been explained in the case of acrack region, the same holds in molten processed regions and refractiveindex change regions as well. Also, though pulse laser light isexplained, the same holds in continuous wave laser light as well. Theforegoing also hold in a fourth embodiment which will be explainedlater.

The laser processing apparatus in accordance with the third embodimentof the present invention will now be explained. FIG. 40 is a schematicdiagram of this laser processing apparatus. The laser processingapparatus 200 will be explained mainly in terms of its differences fromthe laser processing apparatus 100 in accordance with the firstembodiment shown in FIG. 14. The laser processing apparatus 200comprises an ellipticity regulator 201 for adjusting the ellipticity ofpolarization of laser light L emitted from a laser light source 101, anda 90° rotation regulator 203 for adjusting the rotation of polarizationof the laser light L emitted from the ellipticity regulator 201 by about90°.

The ellipticity regulator 201 includes a quarter wave plate 207 shown inFIG. 41. The quarter wave plate 207 can adjust the ellipticity ofelliptically polarized light by changing the angle of direction θ.Namely, when light with linear polarization LP is made incident on thequarter wave plate 207, the transmitted light attains ellipticalpolarization EP with a predetermined ellipticity. The angle of directionis an angle formed between the major axis of the ellipse and the X axis.As mentioned above, a number other than 1 is employed as the ellipticityin this embodiment. The ellipticity regulator 201 can make thepolarization of laser light L become elliptically polarized light EPhaving a desirable ellipticity. The ellipticity is adjusted in view ofthe thickness and material of the object to be processed 1, and thelike.

When irradiating the object to be processed 1 with laser light L havinglinear polarization LP, the laser light L emitted from the laser lightsource 101 is linearly polarized light LP, whereby the ellipticityregulator 201 adjusts the angle of direction θ of the quarter wave plate207 such that the laser light L passes through the quarter wave platewhile being the linearly polarized light LP. Also, the laser lightsource 101 emits linearly polarized laser light L, whereby theellipticity regulator 201 is unnecessary when only laser light of linearpolarization LP is utilized for irradiating the object to be processedwith laser.

The 90° rotation regulator 203 includes a half wave plate 205 as shownin FIG. 42. The half wave plate 205 is a wavelength plate for makingpolarization orthogonal to linearly polarized incident light. Namely,when linearly polarized light LP₁ with an angle of direction of 45° isincident on the half wave plate 205, for embodiment, transmitted lightbecomes linearly polarized light LP₂ rotated by 90° with respect to theincident light LP₁. When rotating the polarization of laser light Lemitted from the ellipticity regulator 201 by 90°, the 90° rotationregulator 203 operates so as to place the half wave plate 205 onto theoptical axis of laser light L. When not rotating the polarization oflaser light L emitted from the ellipticity regulator 201, the 90°rotation regulator 203 operates so as to place the half wave plate 205outside the optical path of laser light L (i.e., at a site where thelaser light L does not pass through the half wave plate 205).

The dichroic mirror 103 is disposed such that the laser light L whoserotation of polarization is regulated by 90° or not by the 90° rotationregulator 203 is incident thereon and that the direction of optical axisof laser light L is changed by 90°. The laser processing apparatus 200comprises a θ-axis stage 213 for rotating the X-Y plane of the mountingtable 107 about the thickness direction of the object to be processed 1.The stage controller 115 regulates not only the movement of stages 109,111, 113, but also the movement of stage 213.

With reference to FIGS. 40 and 43, the laser processing method inaccordance with the third embodiment of the present invention will nowbe explained. FIG. 43 is a flowchart for explaining this laserprocessing method. The object to be processed 1 is a silicon wafer.Steps S101 to S111 are the same as those of the first embodiment shownin FIG. 15.

The ellipticity regulator 201 adjusts the ellipticity of laser light Lhaving linear polarization LP emitted from the laser light source 101(S121). The laser light L having elliptical polarization EP with adesirable ellipticity can be obtained when the angle of direction θ ofthe quarter wave plate is changed in the ellipticity regulator 201.

First, for processing the object to be processed 1 along the Y-axisdirection, the major axis of an ellipse indicative of the ellipticalpolarization EP of laser light L is adjusted so as to coincide with thedirection of the line 5 along which the object is intended to be cutextending in the Y-axis direction of the object to be processed 1(S123). This is achieved by rotating the θ-axis stage 213. Therefore,the θ-axis stage 213 functions as major axis adjusting means or linearpolarization adjusting means.

For processing the object 1 along the Y-axis direction, the 90° rotationregulator 203 carries out adjustment which does not rotate thepolarization of laser light L (S125). Namely, it operates so as to placethe half wave plate to the outside of the optical path of laser light L.

The laser light source 101 generates laser light L, whereas the line 5along which the object is intended to be cut extending in the Y-axisdirection in the surface 3 of the object to be processed 1 is irradiatedwith the laser light L. FIG. 44 is a plan view of the object 1. Theobject 1 is irradiated with the laser light L such that the major axisindicative of the ellipse of elliptical polarization EP of laser lightextends along the rightmost line 5 along which the object is intended tobe cut in the object 1. Since the light-converging point P of laserlight L is positioned within the object 1, molten processed regions areformed only within the object 1. The Y-axis stage 111 is moved along theline 5 along which the object is intended to be cut, so as to form amolten processed region within the object to be processed 1 along theline 5 along which the object is intended to be cut.

Then, the X-axis stage 109 is moved, so as to irradiate the neighboringline 5 along which the object is intended to be cut with laser light L,and a molten processed region is formed within the object 1 along theneighboring line 5 along which the object is intended to be cut in amanner similar to that mentioned above. By repeating this, a moltenprocessed region is formed within the object 1 along the lines alongwhich the object is intended to be cut successively from the right side(S127). FIG. 45 shows the case where the object 1 is irradiated with thelaser light L having linear polarization. Namely, the object 1 isirradiated with laser light such that the direction of linearpolarization LP of laser light extends along the line 5 along which theobject is intended to be cut in the object 1.

Next, the 90° rotation regulator 203 operates so as to place the halfwave plate 205 (FIG. 42) onto the optical axis of laser light L. Thiscarries out adjustment for rotating the polarization of laser lightemitted from the ellipticity regulator 219 by 90° (S219).

Subsequently, the laser light 101 generates laser light L, whereas theline along which the object is intended to be cut extending in theX-axis direction of the surface 3 of the object 1 is irradiated with thelaser light L. FIG. 46 is a plan view of the object 1. The object 1 isirradiated with the laser light L such that the direction of the majoraxis of an ellipse indicative of the elliptical polarization EP of laserlight L extends along the lowest line 5 along which the object isintended to be cut extending in the X-axis direction of the object 1.Since the light-converging point P of laser light L is positioned withinthe object 1, molten processed regions are formed only within the object1. The X-axis stage 109 is moved along the line 5 along which the objectis intended to be cut, so as to form a molten processed region withinthe object 1 extending along the line 5 along which the object isintended to be cut.

Then, the Y-axis stage is moved, such that the immediately upper line 5along which the object is intended to be cut is irradiated with thelaser light L, whereby a molten processed region is formed within theobject 1 along the line 5 along which the object is intended to be cutin a manner similar to that mentioned above. By repeating this,respective molten processed regions are formed within the object 1 alongthe individual lines along which the object is intended to be cutsuccessively from the lower side (S131). FIG. 47 shows the case wherethe object 1 is irradiated with the laser light L having linearpolarization LP.

Then, the object 1 is bent along the lines along which the object isintended to be cut 5, whereby the object 1 is cut (S133). This dividesthe object 1 into silicon chips.

Effects of the third embodiment will be explained. According to thethird embodiment, the object 1 is irradiated with pulse laser light Lsuch that the direction of the major axis of an ellipse indicative ofthe elliptical polarization EP of pulse laser light L extends along theline 5 along which the object is intended to be cut as shown in FIGS. 44and 46. As a consequence, the size of crack spots in the direction ofline 5 along which the object is intended to be cut becomes relativelylarge, whereby crack regions extending along lines along which theobject is intended to be cut can be formed by a smaller number of shots.The third embodiment can efficiently form crack regions as such, thusbeing able to improve the processing speed of the object 1. Also, thecrack spot formed at the shot does not extend in directions other thanthe direction aligning with the line 5 along which the object isintended to be cut, whereby the object 1 can be cut precisely along theline 5 along which the object is intended to be cut. These results aresimilar to those of the fourth embodiment which will be explained later.

Fourth Embodiment

The fourth embodiment of the present invention will be explained mainlyin terms of its differences from the third embodiment. FIG. 48 is aschematic diagram of this laser processing apparatus 300. Among theconstituents of the laser processing apparatus 300, those identical toconstituents of the laser processing apparatus 200 in accordance withthe third embodiment shown in FIG. 40 will be referred to with numeralsidentical thereto without repeating their overlapping explanations.

The laser processing apparatus 300 is not equipped with the 90° rotationregulator 203 of the third embodiment. A θ-axis stage 213 can rotate theX-Y plane of a mounting table 107 about the thickness direction of theobject to be processed 1. This makes the polarization of laser light Lemitted from the ellipticity regulator 201 relatively rotate by 90°.

The laser processing method in accordance with the fourth embodiment ofthe present invention will be explained. Operations of step S101 to stepS123 in the laser processing method in accordance with the thirdembodiment shown in FIG. 43 are carried out in the fourth embodiment aswell. The operation of subsequent step S125 is not carried out, sincethe fourth embodiment is not equipped with the 90° rotation regulator203.

After step S123, the operation of step S127 is carried out. Theoperations carried out so far process the object 1 as shown in FIG. 44in a manner similar to that in the third embodiment. Thereafter, thestage controller 115 regulates the θ-axis stage 213 so as to rotate itby 90°. The rotation of the θ-axis stage 213 rotates the object 1 by 90°in the X-Y plane. Consequently, as shown in FIG. 49, the major axis ofelliptical polarization EP can be caused to align with a line alongwhich the object is intended to be cut intersecting the line 5 alongwhich the object is intended to be cut having already completed themodified region forming step.

Then, like step S127, the object 1 is irradiated with the laser light,whereby molten processed regions are formed within the object to beprocessed 1 along line 5 along which the object is intended to be cutsuccessively from the right side. Finally, as with step S133, the objectis cut, whereby the object 1 is divided into silicon chips.

The third and fourth embodiments of the present invention explained inthe foregoing relate to the forming of modified regions by multiphotonabsorption. However, the present invention may cut the object to beprocessed by irradiating it with laser light while locating itslight-converging point within the object so as to make the major axisdirection of an ellipse indicative of elliptical polarization extendalong a line along which the object is intended to be cut in the objectwithout forming modified regions caused by multiphoton absorption. Thiscan also cut the object along the line along which the object isintended to be cut efficiently.

Fifth Embodiment

In a fifth embodiment of the present invention and sixth and seventhembodiments thereof, which will be explained later, sizes of modifiedspots are controlled by regulating the magnitude of power of pulse laserlight and the size of numerical aperture of an optical system includinga light-converging lens. The modified spot refers to a modified partformed by a single pulse shot of pulse laser light (i.e., one pulselaser irradiation), whereas an assembly of modified spots forms amodified region. The necessity to control the sizes of modified spotswill be explained with respect to crack spots by way of embodiment.

When a crack spot is too large, the accuracy of cutting an object to becut along a line along which the object is intended to be cut decreases,and the flatness of the cross section deteriorates. This will beexplained with reference to FIGS. 50 to 55. FIG. 50 is a plan view of anobject to be processed 1 in the case where crack spots are formedrelatively large by using the laser processing method in accordance withthis embodiment. FIG. 51 is a sectional view taken along LI-LI on theline 5 along which the object is intended to be cut in FIG. 50. FIGS.52, 53, and 54 are sectional views taken along lines LII-LII, LIII-LIII,and LIV-LIV orthogonal to the line 5 along which the object is intendedto be cut in FIG. 50, respectively. As can be seen from these drawings,the deviation in sizes of crack spots 9 becomes greater when the crackspots 90 are too large. Therefore, as shown in FIG. 55, the accuracy ofcutting the object 1 along the line 5 along which the object is intendedto be cut becomes lower. Also, irregularities of cross sections 43 inthe object 1 become so large that the flatness of the cross section 43deteriorates. When crack spots 90 are formed relatively small (e.g., 20μm or less) by using the laser processing apparatus in accordance withthis embodiment, by contrast, crack spots 90 can be formed uniformly andcan be restrained from widening in directions deviating from that of theline along which the object is intended to be cut as shown in FIG. 56.Therefore, as shown in FIG. 57, the accuracy of cutting the object 1along the line 5 along which the object is intended to be cut and theflatness of cross sections 43 can be improved as shown in FIG. 57.

When crack spots are too large as such, precise cutting along a linealong which the object is intended to be cut and cutting for yielding aflat cross-section cannot be carried out. If crack spots are extremelysmall with respect to an object to be processed having a largethickness, however, the object will be hard to cut.

The fact that this embodiment can control sizes of crack spots will beexplained. As shown in FIG. 7, when the peak power density is the same,the size of a crack spot in the case where the light-converging lens hasa magnification of ×10 and an NA of 0.8 is smaller than that of a crackspot in the case where the light-converging lens has a magnification of×50 and an NA of 0.55. The peak power density is proportional to theenergy of laser light per pulse, i.e., the power of pulse laser light,as explained above, whereby the same peak power density means the samelaser light power. When the laser light power is the same while the beamspot cross-sectional area is the same, sizes of crack spots can beregulated so as to become smaller (greater) as the numerical aperture ofa light-converging lens is greater (smaller).

Also, even when the numerical aperture of the light-converging lens isthe same, sizes of crack spots can be regulated so as to become smallerand larger when the laser light power (peak power density) is made lowerand higher, respectively.

Therefore, as can be seen from the graph shown in FIG. 7, sizes of crackspots can be regulated so as to become smaller when the numericalaperture of a light-converging lens is made greater or the laser lightpower is made lower. On the contrary, sizes of crack spots can beregulated so as to become greater when the numerical aperture of alight-converging lens is made smaller or when the laser light power ismade higher.

The crack spot size control will further be explained with reference tothe drawings. The embodiment shown in FIG. 58 is a sectional view of anobject to be processed 1 within which pulse laser light L is convergedby use of a light-converging lens having a predetermined numericalaperture. Regions 41 are those having yielded an electric fieldintensity at a threshold for causing multiphoton absorption or higher bythis laser irradiation. FIG. 59 is a sectional view of a crack spot 90formed due to the multiphoton absorption caused by irradiation with thelaser light L. On the other hand, the embodiment shown in FIG. 60 is asectional view of an object to be processed 1 within which pulse laserlight L is converged by use of a light-converging lens having anumerical aperture greater than that in the embodiment shown in FIG. 58.FIG. 61 is a sectional view of a crack spot 90 formed due to themultiphoton absorption caused by irradiation with the laser light L. Theheight h of crack spot 90 depends on the size of regions 41 in thethickness direction of the object 1, whereas the width w of crack spot90 depends on the size of regions 41 in a direction orthogonal to thethickness direction of the object 1. Namely, when these sizes of regions41 are made smaller and greater, the height h and width w of crack spot90 can be made smaller and greater, respectively. As can be seen whenFIGS. 59 and 61 are compared with each other, in the case where thelaser light power is the same, the sizes of height h and width w ofcrack spot 90 can be regulated so as to become smaller (greater) whenthe numerical aperture of a light-converging lens is made greater(smaller).

The embodiment shown in FIG. 62 is a sectional view of an object to beprocessed 1 within which pulse laser light L having a power lower thanthat in the embodiment shown in FIG. 58 is converged. In the embodimentshown in FIG. 62, since the laser light power is made lower, the area ofregions 41 is smaller than that of regions 41 shown in FIG. 58. FIG. 63is a sectional view of a crack spot 90 formed due to the multiphotonabsorption caused by irradiation with the laser light L. As can be seenwhen FIGS. 59 and 63 are compared with each other, in the case where thenumerical aperture of the light-converging lens is the same, the sizesof height h and width w of crack spot 90 can be regulated so as tobecome smaller (greater) when the laser light power is made lower(higher).

The embodiment shown in FIG. 64 is a sectional view of an object to beprocessed 1 within which pulse laser light L having a power lower thanthat in the embodiment shown in FIG. 60 is converged. FIG. 65 is asectional view of a crack spot 90 formed due to the multiphotonabsorption caused by irradiation with the laser light L. As can be seenwhen FIGS. 59 and 65 are compared with each other, the sizes of height hand width w of crack spot 90 can be regulated so as to become smaller(greater) when the numerical aperture of the light-converging lens ismade greater (smaller) while the laser light power is made lower(higher).

Meanwhile, the regions 41 indicative of those yielding an electric fieldintensity at a threshold for electric field intensity capable of forminga crack spot or higher are restricted to the light-converging point Pand its vicinity due to the following reason: Since a laser light sourcewith a high beam quality is utilized, this embodiment achieves a highconvergence of laser light and can converge light up to about thewavelength of laser light. As a consequence, the beam profile of thislaser light attains a Gaussian distribution, whereby the electric fieldintensity is distributed so as to become the highest at the center ofthe beam and gradually lowers as the distance from the center increases.The laser light is basically converged in the state of a Gaussiandistribution in the process of being converged by a light-converginglens in practice as well. Therefore, the regions 41 are restricted tothe light-converging point P and its vicinity.

As in the foregoing, this embodiment can control sizes of crack spots.Sizes of crack spots are determined in view of a requirement for adegree of precise cutting, a requirement for a degree of flatness incross sections, and the magnitude of thickness of the object to beprocessed. Sizes of crack spots can be determined in view of thematerial of an object to be processed as well. This embodiment cancontrol sizes of modified spots, thus making it possible to carry outprecise cutting along a line along which the object is intended to becut and yield a favorable flatness in cross sections by making modifiedspots smaller for objects to be processed having a relatively smallthickness. Also, by making modified spots greater, it enables cutting ofobjects to be processed having a relatively large thickness.

There are cases where an object to be processed has respectivedirections easy and hard to cut due to the crystal orientation of theobject, for embodiment. When cutting such an object, the size of crackspots 90 formed in the easy-to-cut direction is made greater as shown inFIGS. 56 and 57, for embodiment. When the direction of a line alongwhich the object is intended to be cut orthogonal to the line 5 alongwhich the object is intended to be cut is a hard-to-cut direction, onthe other hand, the size of crack spots 90 formed in this direction ismade greater as shown in FIGS. 57 and 66. Here, FIG. 66 is a sectionalview of the object 1 shown in FIG. 57 taken along LXVI-LXVI. Hence, aflat cross section can be obtained in the easy-to-cut direction, whilecutting is possible in the hard-to-cut direction as well.

Though the fact that sizes of modified spots are controllable has beenexplained in the case of crack spots, the same holds in melting spotsand refractive index change spots. For embodiment, the power of pulselaser light can be expressed by energy per pulse (J), or average output(W) which is a value obtained by multiplying the energy per pulse by thefrequency of laser light. The foregoing holds in sixth and seventhembodiments which will be explained later.

The laser processing apparatus in accordance with the fifth embodimentof the present invention will be explained. FIG. 67 is a schematicdiagram of this laser processing apparatus 400. The laser processingapparatus 400 will be explained mainly in terms of its differences fromthe laser processing apparatus 100 in accordance with the firstembodiment shown in FIG. 14.

The laser processing apparatus 400 comprises a power regulator 401 foradjusting the power of laser light L emitted from a laser light source101. The power regulator 401 comprises, for embodiment, a plurality ofND (neutral density) filters, and a mechanism for moving the individualND filters to positions perpendicular to the optical axis of the laserlight L and to the outside of the optical path of laser light L. An NDfilter is a filter which reduces the intensity of light without changingthe relative spectral distribution of energy. A plurality of ND filtershave respective extinction factors different from each other. By usingone of a plurality of ND filters or combining some of them, the powerregulator 401 adjusts the power of laser light L emitted from the laserlight source 101. Here, a plurality of ND filters may have the sameextinction factor, and the power regulator 401 may change the number ofND filters to be moved to positions perpendicular to the optical axis oflaser light L, so as to adjust the power of laser light L emitted fromthe laser light source 101.

The power regulator 401 may comprise a polarization filter disposedperpendicular to the optical axis of linearly polarized laser light L,and a mechanism for rotating the polarization filter about the opticalaxis of laser light L by a desirable angle. Rotating the polarizationfilter about the optical axis by a desirable angle in the powerregulator 401 adjusts the power of laser light L emitted from the laserlight source 101.

Here, the driving current for a pumping semiconductor laser in the laserlight source 101 can be regulated by a laser light source controller 102which is an embodiment of driving current control means, so as toregulate the power of laser light L emitted from the laser light source101. Therefore, the power of laser light L can be adjusted by at leastone of the power regulator 401 and laser light source controller 102. Ifthe size of a modified region can attain a desirable value due to theadjustment of power of laser light L by the laser light sourcecontroller 102 alone, the power regulator 401 is unnecessary. The poweradjustment explained in the foregoing is effected when an operator ofthe laser processing apparatus inputs the magnitude of power into anoverall controller 127, which will be explained later, by using akeyboard or the like.

The laser processing apparatus 400 further comprises a dichroic mirror103 disposed such that the laser light L whose power is adjusted by thepower regulator 401 is incident thereon whereas the orientation of theoptical axis of laser light L is changed by 90°; a lens selectingmechanism 403 including a plurality of light-converging lenses forconverging the laser light L reflected by the dichroic mirror 103; and alens selecting mechanism controller 405 for controlling the lensselecting mechanism 403.

The lens selecting mechanism 403 comprises light-converging lenses 105a, 105 b, 105 c, and a support plate 407 for supporting them. Thenumerical apertures of respective optical systems including thelight-converging lenses 105 a, 105 b, 105 c differ from each other.According to a signal from the lens selecting mechanism controller 405,the lens selecting mechanism 403 rotates the support plate 407, therebycausing a desirable light-converging lens among the light-converginglenses 105 a, 105 b, 105 c to be placed onto the optical axis of laserlight L. Namely, the lens selecting mechanism 403 is of revolver type.

The number of light-converging lenses attached to the lens selectingmechanism 403 is not restricted to 3 but may be other numbers. When theoperator of the laser processing apparatus inputs a size of numericalaperture or an instruction for choosing one of the light-converginglenses 105 a, 105 b, 105 c into the overall controller 127, which willbe explained later, by using a keyboard or the like, thelight-converging lens is chosen, namely, the numerical aperture ischosen.

Mounted on the mounting table 107 of the laser processing apparatus 400is an object to be processed 1 irradiated with the laser light Lconverged by one of the light-converging lenses 105 a to 105 c which isdisposed on the optical axis of laser light L.

The overall controller 127 is electrically connected to the powerregulator 401. FIG. 67 does not depict it. When the magnitude of poweris fed into the overall controller 127, the latter controls the powerregulator 401, thereby adjusting the power.

FIG. 68 is a block diagram showing a part of an embodiment of theoverall controller 127. The overall controller 127 comprises a sizeselector 411, a correlation storing section 413, and an image preparingsection 415. The operator of the laser processing apparatus inputs themagnitude of power of pulse laser light or the size of numericalaperture of the optical system including the light-converging lens tothe size selector 411 by using a keyboard or the like. In thisembodiment, the input may choose one of the light-converging lenses 105a, 105 b, 105 c instead of the numerical aperture size being directlyinputted. In this case, the respective numerical apertures of thelight-converging lenses 105 a, 105 b, 105 c are registered in theoverall controller 127 beforehand, and data of the numerical aperture ofthe optical system including the chosen light-converging lens isautomatically fed into the size selector 411.

The correlation storing section 413 has stored the correlation betweenthe set of pulse laser power magnitude and numerical aperture size andthe size of modified spot beforehand. FIG. 69 is an embodiment of tableshowing this correlation. In this embodiment, respective numericalapertures of the optical systems including the light-converging lenses105 a, 105 b, 105 c are registered in the column for numerical aperture.In the column for power, magnitudes of power attained by the powerregulator 401 are registered. In the column for size, sizes of modifiedspots formed by combinations of powers of their corresponding sets andnumerical apertures are registered. For embodiment, the modified spotformed when the power is 1.24×10¹¹ (W/cm²) while the numerical apertureis 0.55 has a size of 120 μm. The data of this correlation can beobtained by carrying out experiments explained in FIGS. 58 to 65 beforelaser processing, for embodiment.

When the magnitude of power and numerical aperture size are fed into thesize selector 411, the latter chooses the set having their correspondingvalues from the correlation storing section 413, and sends data of sizecorresponding to this set to the monitor 129. As a consequence, the sizeof a modified spot formed at thus inputted magnitude of power andnumerical aperture size is displayed on the monitor 129. If there is noset corresponding to these values, size data corresponding to a sethaving the closest values is sent to the monitor 129.

The data of size corresponding to the set chosen by the size selector411 is sent from the size selector 411 to the image preparing section415. According to this size data, the image preparing section 415prepares image data of a modified spot in this size, and sends thusprepared data to the monitor 129. As a consequence, an image of themodified spot is also displayed on the monitor 129. Hence, the size andform of modified spot can be seen before laser processing.

The size of numerical aperture may be made variable while the magnitudeof power is fixed. The table in this case will be as shown in FIG. 70.For embodiment, the modified spot formed when the numerical aperture is0.55 while the power is fixed at 1.49×10¹¹ (W/cm²) has a size of 150 μm.Alternatively, the magnitude of power may be made variable while thesize of numerical aperture is fixed. The table in this case will be asshown in FIG. 71. For embodiment, the modified spot formed when thepower is fixed at 1.19×10¹¹ (W/cm²) while the numerical aperture isfixed at 0.8 has a size of 30 μm.

The laser processing method in accordance with the fifth embodiment ofthe present invention will now be explained with reference to FIG. 67.The object to be processed 1 is a silicon wafer. In the fifthembodiment, operations of steps S101 to S111 are carried out as in thelaser processing method in accordance with the first embodiment shown inFIG. 15.

After step S111, the magnitude of power and numerical aperture size arefed into the overall controller 127 as explained above. According to thedata of power inputted, the power of laser light L is adjusted by thepower regulator 401. According to the data of numerical apertureinputted, the lens selecting mechanism 403 chooses a light-converginglens by way of the lens selecting mechanism controller 405, therebyadjusting the numerical aperture. These data are also fed into the sizeselector 411 of the overall controller 127 (FIG. 68). As a consequence,the size and form of a melting spot formed within the object 1 uponirradiation of one pulse of laser light L are displayed on the monitor129.

Then, operations of steps S113 to S115 are carried out as in the laserprocessing method in accordance with the first embodiment shown in FIG.15. This divides the object 1 into silicon chips.

Sixth Embodiment

A sixth embodiment of the present invention will now be explained mainlyin terms of its differences from the fifth embodiment. FIG. 72 is aschematic diagram of this laser processing apparatus 500. Among theconstituents of the laser processing apparatus 500, those identical toconstituents of the laser processing apparatus 400 in accordance withthe fifth embodiment shown in FIG. 67 are referred to with numeralsidentical thereto without repeating their overlapping explanations.

In the laser processing apparatus 500, a beam expander 501 is disposedon the optical axis of laser light L between a power regulator 401 and adichroic mirror 103. The beam expander 501 has a variable magnification,and is regulated by the beam expander 501 so as to increase the beamdiameter of laser light L. The beam expander 501 is an embodiment ofnumerical aperture regulating means. The laser processing apparatus 500is equipped with a single light-converging lens 105 instead of the lensselecting mechanism 403.

The operations of the laser processing apparatus 500 differ from thoseof the laser processing apparatus of the fifth embodiment in theadjustment of numerical aperture based on the magnitude of numericalaperture fed into the overall controller 127. This will be explained inthe following. The overall controller 127 is electrically connected tothe beam expander 501. FIG. 72 does not depict this. When the size ofnumerical aperture is fed into the overall controller 127, the lattercarries out control for changing the magnitude of beam expander 501.This regulates the magnification of beam diameter of the laser light Lincident on the light-converging lens 105. Therefore, with only onelight-converging lens 105, adjustment for increasing the numericalaperture of the optical system including the light-converging lens 105is possible. This will be explained with reference to FIGS. 73 and 74.

FIG. 73 is a view showing the convergence of laser light L effected bythe light-converging lens 105 when the beam expander 501 is notprovided. On the other hand, FIG. 74 is a view showing the convergenceof laser light L effected by the light-converging lens 105 when the beamexpander 501 is provided. As can be seen when FIGS. 73 and 74 arecompared with each other, the sixth embodiment can achieve adjustment soas to increase the numerical aperture with reference to the numericalaperture of the optical system including the light-converging lens 105in the case where the beam expander 501 is not provided.

Seventh Embodiment

A seventh embodiment of the present invention will now be explainedmainly in terms of its differences from the fifth and sixth embodiments.FIG. 75 is a schematic diagram of this laser processing apparatus 600.Among the constituents of the laser processing apparatus 600, thoseidentical to constituents of the laser processing apparatus inaccordance with the fifth and sixth embodiments are referred to withnumerals identical thereto without repeating their overlappingexplanations.

In the laser processing apparatus 600, an iris diaphragm 601 is disposedon the optical axis of laser light L instead of the beam expander 501between a dichroic mirror 103 and a light-converging lens 105. Changingthe aperture size of the iris diaphragm 601 adjusts the effectivediameter of the light-converging lens 105. The iris diaphragm 601 is anembodiment of numerical aperture regulating means. The laser processingapparatus 600 further comprises an iris diaphragm controller 603 forchanging the aperture size of the iris diaphragm 601. The iris diaphragmcontroller 603 is controlled by an overall controller 127.

The operations of the laser processing apparatus 600 differ from thoseof the laser processing apparatus of the fifth and sixth embodiments inthe adjustment of numerical aperture based on the size of numericalaperture fed into the overall controller 127. According to the inputtedsize of numerical aperture, the laser processing apparatus 600 changesthe size of aperture of the iris diaphragm 601, thereby carrying outadjustment for decreasing the effective diameter of the light-converginglens 105. Therefore, with only one light-converging lens 105, adjustmentfor decreasing the numerical aperture of the optical system includingthe light-converging lens 105 is possible. This will be explained withreference to FIGS. 76 and 77.

FIG. 76 is a view showing the convergence of laser light L effected bythe light-converging lens 105 when no iris diaphragm is provided. On theother hand, FIG. 77 is a view showing the convergence of laser light Leffected by the light-converging lens 105 when the iris diaphragm 601 isprovided. As can be seen when FIGS. 76 and 77 are compared with eachother, the seventh embodiment can achieve adjustment so as to increasethe numerical aperture with reference to the numerical aperture of theoptical system including the light-converging lens 105 in the case wherethe iris diaphragm is not provided.

Modified embodiments of the fifth to seventh embodiments of the presentinvention will now be explained. FIG. 78 is a block diagram of theoverall controller 127 provided in a modified embodiment of the laserprocessing apparatus in accordance with this embodiment. The overallcontroller 127 comprises a power selector 417 and a correlation storingsection 413. The correlation storing section 413 has already stored thecorrelation data shown in FIG. 71. An operator of the laser processingapparatus inputs a desirable size of a modified spot to the powerselector 417 by a keyboard or the like. The size of modified spot isdetermined in view of the thickness and material of the object to bemodified and the like. According to this input, the power selector 417chooses a power corresponding to the value of size identical to thusinputted size from the correlation storing section 413, and sends it tothe power regulator 401. Therefore, when the laser processing apparatusregulated to this magnitude of power is used for laser processing, amodified spot having a desirable size can be formed. The data concerningthis magnitude of power is also sent to the monitor 129, whereby themagnitude of power is displayed. In this embodiment, the numericalaperture is fixed while power is variable. If no size at the valueidentical to that of thus inputted value is stored in the correlationstoring section 413, power data corresponding to a size having theclosest value is sent to the power regulator 401 and the monitor 129.This is the same in the modified embodiments explained in the following.

FIG. 79 is a block diagram of the overall controller 127 provided inanother modified embodiment of the laser processing apparatus inaccordance with this embodiment. The overall controller 127 comprises anumerical aperture selector 419 and a correlation storing section 413.It differs from the modified embodiment of FIG. 78 in that the numericalaperture is chosen instead of the power. The correlation storing section413 has already stored the data shown in FIG. 70. An operator of thelaser processing apparatus inputs a desirable size of a modified spot tothe numerical aperture selector 419 by using a keyboard or the like. Asa consequence, the numerical aperture selector 419 chooses a numericalaperture corresponding to a size having a value identical to that of theinputted size from the correlation storing section 413, and sends dataof this numerical aperture to the lens selecting mechanism controller405, beam expander 501, or iris diaphragm controller 603. Therefore,when the laser processing apparatus regulated to this size of numericalaperture is used for laser processing, a modified spot having adesirable size can be formed. The data concerning this numericalaperture is also sent to the monitor 129, whereby the size of numericalaperture is displayed. In this embodiment, the power is fixed whilenumerical aperture is variable.

FIG. 80 is a block diagram of the overall controller 127 provided instill another modified embodiment of the laser processing apparatus inaccordance with this embodiment. The overall controller 127 comprises aset selector 421 and a correlation storing section 413. It differs fromthe embodiments of FIGS. 78 and 79 in that both power and numericalaperture are chosen. The correlation storing section 413 has stored thecorrelation between the set of power and numerical aperture and the sizein FIG. 69 beforehand. An operator of the laser processing apparatusinputs a desirable size of a modified spot to the set selector 421 byusing a keyboard or the like. As a consequence, the set selector 421chooses a set of power and numerical aperture corresponding to thusinputted size from the correlation storing section 413. Data of power inthus chosen set is sent to the power regulator 401. On the other hand,data of numerical aperture in the chosen set is sent to the lensselecting mechanism controller 405, beam expander 501, or iris diaphragmcontroller 603. Therefore, when the laser processing apparatus regulatedto the power and numerical aperture of this set is used for laserprocessing, a modified spot having a desirable size can be formed. Thedata concerning the magnitude of power and size of numerical aperture isalso sent to the monitor 129, whereby the magnitude of power and size ofnumerical aperture is displayed.

These modified embodiments can control sizes of modified spots.Therefore, when the size of a modified spot is made smaller, the objectto be processed can precisely be cut along a line along which the objectis intended to be cut therein, and a flat cross section can be obtained.When the object to be cut has a large thickness, the size of modifiedspot can be enhanced, whereby the object can be cut.

Eighth Embodiment

An eighth embodiment of the present invention controls the distancebetween a modified spot formed by one pulse of laser light and amodified spot formed by the next one pulse of pulse laser light byregulating the magnitude of a repetition frequency of pulse laser lightand the magnitude of relative moving speed of the light-converging pointof pulse laser light. Namely, it controls the distance between adjacentmodified spots. In the following explanation, the distance is assumed tobe a pitch p. The control of pitch p will be explained in terms of acrack region by way of embodiment.

Let f (Hz) be the repetition frequency of pulse laser light, and v(mm/sec) be the moving speed of the X-axis stage or Y-axis stage of theobject to be processed. The moving speeds of these stages areembodiments of relative moving speed of the light-converging point ofpulse laser light. The crack part formed by one shot of pulse laserlight is referred to as crack spot. Therefore, the number n of crackspots formed per unit length of the line 5 along which the object isintended to be cut is as follows:

n=f/v.

The reciprocal of the number n of crack spots formed per unit lengthcorresponds to the pitch p:

p=1/n.

Hence, the pitch p can be controlled when at least one of the magnitudeof repetition frequency of pulse laser light and the magnitude ofrelative moving speed of the light-converging point is regulated.Namely, the pitch p can be controlled so as to become smaller when therepetition frequency f(Hz) is increased or when the stage moving speedv(mm/sec) is decreased. By contrast, the pitch p can be controlled so asto become greater when the repetition frequency f(Hz) is decreased orwhen the stage moving speed v(mm/sec) is increased.

Meanwhile, there are three ways of relationship between the pitch p andcrack spot size in the direction of line 5 along which the object isintended to be cut as shown in FIGS. 81 to 83. FIGS. 81 to 83 are planviews of an object to be processed along the line 5 along which theobject is intended to be cut, which is formed with a crack region by thelaser processing in accordance with this embodiment. A crack spot 90 isformed by one pulse of pulse laser light. Forming a plurality of crackspots 90 aligning each other along the line 5 along which the object isintended to be cut yields a crack region 9.

FIG. 81 shows a case where the pitch p is greater than the size d. Thecrack region 9 is formed discontinuously along the line 5 along whichthe object is intended to be cut within the object to be processed. FIG.82 shows a case where the pitch p substantially equals the sized. Thecrack region 9 is formed continuously along the line 5 along which theobject is intended to be cut within the object to be processed. FIG. 83shows a case where the pitch p is smaller than the size d. The crackregion 9 is formed continuously along the line 5 along which the objectis intended to be cut within the object to be processed.

In FIG. 81, the crack region 9 is not continuous along the line 5 alongwhich the object is intended to be cut, whereby the part of line 5 alongwhich the object is intended to be cut keeps a strength to some extent.Therefore, when carrying out a step of cutting the object to beprocessed after laser processing, handling of the object becomes easier.In FIGS. 82 and 83, the crack region 9 is continuously formed along theline 5 along which the object is intended to be cut, which makes it easyto cut the object while using the crack region 9 as a starting point.

The pitch p is made greater than the size d in FIG. 81, andsubstantially equals the size d in FIG. 82, whereby regions generatingmultiphoton absorption upon irradiation with pulse laser light can beprevented from being superposed on crack spots 90 which have alreadybeen formed. As a result, deviations in sizes of crack spots 90 can bemade smaller. Namely, the inventor has found that, when a regiongenerating multiphoton absorption upon irradiation with pulse laserlight is superposed on crack spots 90 which have already been formed,deviations in sizes of crack spots 90 formed in this region becomegreater. When deviations in sizes of crack spots 90 become greater, itbecomes harder to cut the object along a line along which the object isintended to be cut precisely, and the flatness of cross sectiondeteriorates. In FIGS. 81 and 82, deviations in sizes of crack spots canbe made smaller, whereby the object to be processed can be cut along theline along which the object is intended to be cut precisely, while crosssections can be made flat.

As explained in the foregoing, the eighth embodiment of the presentinvention can control the pitch p by regulating the magnitude ofrepetition frequency of pulse laser light or magnitude of relativemoving speed of the light-converging point of pulse laser light. Thisenables laser processing in conformity to the object to be processed bychanging the pitch p in view of the thickness and material of the objectand the like.

Though the fact that the pitch p can be controlled is explained in thecase of crack spots, the same holds in melting spots and refractiveindex change spots. However, there are no problems even when meltingspots and refractive index change spots are superposed on those whichhave already been formed. The relative movement of the light-convergingpoint of pulse laser light may be realized by a case where the object tobe processed is moved while the light-converging point of pulse laserlight is fixed, a case where the light-converging point of pulse laserlight is moved while the object is fixed, a case where the object andthe light-converging point of pulse laser light are moved in directionsopposite from each other, and a case where the object and thelight-converging point of pulse laser light are moved in the samedirection with their respective speeds different from each other.

With reference to FIG. 14, the laser processing apparatus in accordancewith the eighth embodiment of the present invention will be explainedmainly in terms of its differences from the laser processing apparatus100 in accordance with the first embodiment shown in FIG. 14. The laserlight source 101 is a Q-switch laser. FIG. 84 is a schematic diagram ofthe Q-switch laser provided in a laser light source 101. The Q-switchlaser comprises mirrors 51, 53 which are disposed with a predeterminedgap therebetween, a laser medium 55 disposed between the mirrors 51 and53, a pumping source 57 for applying a pumping input to the laser medium55, and a Q-switch 59 disposed between the laser medium 55 and themirror 51. The material of the laser medium 55 is Nd:YAG, forembodiment.

A pumping input is applied from the pumping source 57 to the lasermedium 55 in a state where the loss in a resonator is made high byutilizing the Q-switch 59, whereby the population inversion of the lasermedium 55 is raised to a predetermined value. Thereafter, the Q-switch59 is utilized for placing the resonator into a state with a low loss,so as to oscillate the accumulated energy instantaneously and generatepulse laser light L. A signal S (e.g., a change in a repetitionfrequency of an ultrasonic pulse) from a laser light source controller102 controls the Q-switch 59 so as to make it attain a high state.Therefore, the signal S from the laser light source controller 102 canregulate the repetition frequency of pulse laser light L emitted fromthe laser light source 101. The laser light source controller 102 is anembodiment of frequency adjusting means. The repetition frequency isregulated when an operator of the laser processing apparatus inputs themagnitude of repetition frequency to an overall controller 127, whichwill be explained later, by using a keyboard or the like. The foregoingare details of the laser light source 101.

During the laser processing, the object to be processed 1 is moved inthe X- or Y-axis direction, so as to form a modified region along a linealong which the object is intended to be cut. Therefore, when forming amodified region in the X-axis direction, the speed of relative movementof the light-converging point of laser light can be adjusted byregulating the moving speed of the X-axis stage 109. When forming amodified region in the Y-axis direction, on the other hand, the speed ofrelative movement of the light-converging point of laser light can beadjusted by regulating the moving speed of the Y-axis stage 111. Theadjustment of the respective moving speeds of these stages is controlledby the stage controller 115. The stage controller 115 is an embodimentof speed adjusting means. The speed is regulated when the operator oflaser processing apparatus inputs the magnitude of speed to the overallcontroller 127, which will be explained later, by using a keyboard orthe like. The speed of relative movement of the light-converging pointof pulse laser light can be adjusted when, while the light-convergingpoint P is made movable, its moving speed is regulated.

The overall controller 127 of the laser processing apparatus inaccordance with the eighth embodiment further adds other functions tothe overall controller 127 of the laser processing apparatus inaccordance with the first embodiment. FIG. 85 is a block diagram showinga part of an embodiment of the overall controller 127 of the laserprocessing apparatus in accordance with the eighth embodiment. Theoverall controller 127 comprises a distance calculating section 141, asize storing section 143, and an image preparing section 145. To thedistance calculating section 141, the magnitude of repetition frequencyof pulse laser light and respective magnitudes of moving speeds of thestages 109, 111 are inputted. These inputs are effected by the operatorof laser processing apparatus using a keyboard or the like.

The distance calculating section 141 calculates the distance (pitch)between adjacent spots by utilizing the above-mentioned expressions(n=f/v, and p=1/n). The distance calculating section 141 sends thisdistance data to the monitor 129. As a consequence, the distance betweenmodified spots formed at the inputted magnitudes of frequency and speedis displayed on the monitor 129.

The distance data is also sent to the image preparing section 145. Thesize storing section 143 has already stored therein sizes of modifiedspots formed in this laser processing apparatus. According to thedistance data and the size data stored in the size storing section 143,the image preparing section 145 prepares image data of a modified regionformed by the distance and size, and sends thus prepared image data tothe monitor 129. As a consequence, an image of the modified region isalso displayed on the monitor 129. Hence, the distance between adjacentmodified spots and the form of modified region can be seen before laserprocessing.

Though the distance calculating section 141 calculates the distancebetween modified spots by utilizing the expressions (n=f/v, and p=1/n),the following procedure may also be taken. First, a table havingregistered the relationship between the magnitude of repetitionfrequency, the moving speeds of stages 109, 111, and the distancebetween modified spots beforehand is prepared, and the distancecalculating section 141 is caused to store data of this table. When themagnitude of repetition frequency and the magnitudes of moving speeds ofstages 109, 111 are fed into the distance calculating section 141, thelatter reads out from the above-mentioned table the distance betweenmodified spots in the modified spots formed under the condition of thesemagnitude.

Here, the magnitudes of stage moving speeds may be made variable whilethe magnitude of repetition frequency is fixed. On the contrary, themagnitude of repetition frequency may be made variable while themagnitudes of stage moving speeds are fixed. Also, in these cases, theabove-mentioned expressions and table are used in the distancecalculating section 141 for carrying out processing for causing themonitor 129 to display the distance between modified spots and an imageof the modified region.

As in the foregoing, the overall controller 127 shown in FIG. 85 inputsthe magnitude of repetition frequency and the stage moving speeds,thereby calculating the distance between adjacent modified spots.Alternatively, a desirable distance between adjacent modified spots maybe inputted, and the magnitude of repetition frequency and magnitudes ofstage moving speeds may be controlled. This procedure will be explainedin the following.

FIG. 86 is a block diagram showing a part of another embodiment of theoverall controller 127 provided in the eighth embodiment. The overallcontroller 127 comprises a frequency calculating section 147. Theoperator of laser processing apparatus inputs the magnitude of distancebetween adjacent modified spots to the frequency calculating section 147by using a keyboard or the like. The magnitude of distance is determinedin view of the thickness and material of the object to be processed andthe like. Upon this input, the frequency calculating section 147calculates a frequency for attaining this magnitude of distanceaccording to the above-mentioned expressions and tables. In thisembodiment, the stage moving speeds are fixed. The frequency calculatingsection 147 sends thus calculated data to the laser light sourcecontroller 102. When the object to be processed is subjected to laserprocessing by the laser processing apparatus regulated to this magnitudeof frequency, the distance between adjacent modified spots can attain adesirable magnitude. Data of this magnitude of frequency is also sent tothe monitor 129, whereby this magnitude of frequency is displayed.

FIG. 87 is a block diagram showing a part of still another embodimentthe overall controller 127 provided in the eighth embodiment. Theoverall controller 127 comprises a speed calculating section 149. In amanner similar to that mentioned above, the magnitude of distancebetween adjacent modified spots is fed into the speed calculatingsection 149. Upon this input, the speed calculating section 149calculates a stage moving speed for attaining this magnitude of distanceaccording to the above-mentioned expressions and tables. In thisembodiment, the repetition frequency is fixed. The speed calculatingsection 149 sends thus calculated data to the stage controller 115. Whenthe object to be processed is subjected to laser processing by the laserprocessing apparatus regulated to this magnitude of stage moving speed,the distance between adjacent modified spots can attain a desirablemagnitude. Data of this magnitude of stage moving speed is also sent tothe monitor 129, whereby this magnitude of stage moving speed isdisplayed.

FIG. 88 is a block diagram showing a part of still another embodiment ofthe overall controller 127 provided in the eighth embodiment. Theoverall controller 127 comprises a combination calculating section 151.It differs from the cases of FIGS. 86 and 87 in that both repetitionfrequency and stage moving speed are calculated. In a manner similar tothat mentioned above, the distance between adjacent modified spots isfed into the combination calculating section 151. According to theabove-mentioned expressions and tables, the combination calculatingsection 151 calculates a repetition frequency and a stage moving speedfor attaining this magnitude of distance.

The combination calculating section 151 sends thus calculated data tothe stage controller 115. The laser light source controller 102 adjuststhe laser light source 101 so as to attain the calculated magnitude ofrepetition frequency. The stage controller 115 adjusts the stages 109,111 so as to attain the calculated magnitude of stage moving speed. Whenthe object to be processed is subjected to laser processing by thusregulated laser processing apparatus, the distance between adjacentmodified spots can attain a desirable magnitude. Data of thus calculatedmagnitude of repetition frequency and magnitude of stage moving speedare also sent to the monitor 129, whereby thus calculated values aredisplayed.

The laser processing method in accordance with the eighth embodiment ofthe present invention will now be explained. The object to be processed1 is a silicon wafer. In the eighth embodiment, operations from stepsS101 to S111 are carried out in a manner similar to that of the laserprocessing method in accordance with the first embodiment shown in FIG.15.

After step S111, the distance between adjacent melting spots in themelting spots formed by one pulse of pulse laser, i.e., the magnitude ofpitch p, is determined. The pitch p is determined in view of thethickness and material of the object 1 and the like. The magnitude ofpitch p is fed into the overall controller 127 shown in FIG. 88.

Then, in a manner similar to that of the laser processing method inaccordance with the first embodiment shown in FIG. 15, operations ofstep S113 to S115 are carried out. This divides the object 1 intosilicon chips.

As explained in the foregoing, the eighth embodiment can control thedistance between adjacent melting spots by regulating the magnitude ofrepetition frequency of pulse laser light, and regulating the magnitudesof moving speeds of X-axis stage 109 and Y-axis stage 111. Changing themagnitude of distance in view of the thickness and material of theobject 1 and the like enables processing in conformity to the aimedpurpose.

Ninth Embodiment

A ninth embodiment of the present invention changes the position of thelight-converging point of laser light irradiating the object to beprocessed in the direction of incidence to the object, thereby forming aplurality of modified regions aligning in the direction of incidence.

Forming a plurality of modified regions will be explained in terms of acrack region by way of embodiment. FIG. 89 is a perspective view of anobject to be processed 1 formed with two crack regions 9 within theobject 1 by using the laser processing method in accordance with theninth embodiment of the present invention.

A method of forming two crack regions 9 will be explained in brief.First, the object 1 is irradiated with pulse laser light L, while thelight-converging point of pulse laser light L is located within theobject 1 near its rear face 21 and is moved along a line 5 along whichthe object is intended to be cut. This forms a crack region 9 (9A) alongthe line 5 along which the object is intended to be cut within theobject 1 near the rear face 21. Subsequently, the object 1 is irradiatedwith the pulse laser light L, while the light-converging point of pulselaser light L is located within the object 1 near its surface 3 and ismoved along the line 5 along which the object is intended to be cut.This forms a crack region 9 (9B) along the line 5 along which the objectis intended to be cut within the object 1 near the surface 3.

Then, as shown in FIG. 90, cracks 91 naturally grow from the crackregions 9A, 9B. Specifically, the cracks 91 naturally grow from thecrack region 9A toward the rear face 21, from the crack region 9A (9B)toward the crack region 9B (9A), and from the crack region 9B toward thesurface 3. This can form cracks 9 elongated in the thickness directionof the object in the surface of object 1 extending along the line 5along which the object is intended to be cut, i.e., the surface tobecome a cross section. Hence, the object 1 can be cut along the line 5along which the object is intended to be cut by artificially applying arelatively small force thereto or naturally without applying such aforce.

As in the foregoing, the ninth embodiment forms a plurality of crackregions 9, thereby increasing the number of locations to become startingpoints when cutting the object 1. As a consequence, the ninth embodimentmakes it possible to cut the object 1 even in the cases where the object1 has a relatively large thickness, the object 1 is made of a materialin which cracks 91 are hard to grow after forming the crack regions 9,and so forth.

When cutting is difficult by two crack regions 9 alone, three or morecrack regions 9 are formed. For embodiment, as shown in FIG. 91, a crackregion 9C is formed between the crack region 9A and crack region 9B.Cutting can also be achieved in a direction orthogonal to the thicknessdirection of the object 1 as long as it is the direction of incidence oflaser light as shown in FIG. 92.

Preferably, in the ninth embodiment of the present invention, aplurality of crack regions 9 are successively formed from the sidefarther from the entrance face (e.g., surface 3) of the object to beprocessed on which the pulse laser light L is incident. For embodiment,in FIG. 89, the crack region 9A is formed first, and then the crackregion 9B is formed. If the crack regions 9 are formed successively fromthe side closer to the entrance face, the pulse laser L irradiated atthe time of forming the crack region 9 to be formed later will bescattered by the crack region 9 formed earlier. As a consequence,deviations occur in sizes of the crack part (crack spot) formed by oneshot of pulse laser light L constituting the crack region 9 formedlater. Hence, the crack region 9 formed later cannot be formeduniformly. Forming the crack regions 9 successively from the sidefarther from the entrance face does not generate the above-mentionedscattering, whereby the crack region 9 formed later can be formeduniformly.

However, the order of forming a plurality of crack regions 9 in theninth embodiment of the present invention is not restricted to thatmentioned above. They may be formed successively from the side closer tothe entrance face of the object to be processed, or formed randomly. Inthe random forming, for embodiment in FIG. 91, the crack region 9C isformed first, then the crack region 9B, and finally the crack region 9Ais formed by reversing the direction of incidence of laser light.

Though the forming of a plurality of modified regions is explained inthe case of crack regions, the same holds in molten processed regionsand refractive index change regions. Though the explanation relates topulse laser light, the same holds for continuous wave laser light.

The laser processing apparatus in accordance with the ninth embodimentof the present invention has a configuration similar to that of thelaser processing apparatus 100 in accordance with the first embodimentshown in FIG. 14. In the ninth embodiment, the position oflight-converging point P in the thickness direction of the object to beprocessed 1 is adjusted by the Z-axis stage 113. This can adjust thelight-converging point P so as to locate it at a position closer to orfarther from the entrance face (surface 3) than is a half thicknessposition in the thickness direction of the object to be processed 1, andat a substantially half thickness position.

Here, adjustment of the position of light-converging point P in thethickness direction of the object to be processed caused by the Z-axisstage will be explained with reference to FIGS. 93 and 94. In the ninthembodiment of the present invention, the position of light-convergingpoint of laser light in the thickness direction of the object to beprocessed is adjusted so as to be located at a desirable position withinthe object with reference to the surface (entrance face) of the object.FIG. 93 shows the state where the light-converging point P of laserlight L is positioned at the surface 3 of the object 1. When the Z-axisstage is moved by z toward the light-converging lens 105, thelight-converging point P moves from the surface 3 to the inside of theobject 1 as shown in FIG. 94. The amount of movement of light-convergingpoint P within the object 1 is Nz (where N is the refractive index ofthe object 1 with respect to the laser light L). Hence, when the Z-axisstage is moved in view of the refractive index of the object 1 withrespect to the laser light L, the position of light-converging point Pin the thickness direction of the object 1 can be controlled. Namely, adesirable position of the light-converging point P in the thicknessdirection of the object 1 is defined as the distance (Nz) from thesurface 3 to the inside of the object 1. The object 1 is moved in thethickness direction by the amount of movement (z) obtained by dividingthe distance (Nz) by the above-mentioned refractive index (N). This canlocate the light-converging point P at the desirable position.

As explained in the first embodiment, the stage controller 115 controlsthe movement of the Z-axis stage 113 according to focal point data, suchthat the focal point of visible light is located at the surface 3. Thelaser processing apparatus 1 is adjusted such that the light-convergingpoint P of laser light L is positioned at the surface 3 at the positionof Z-axis stage 113 where the focal point of visible light is located atthe surface 3. Data of the amount of movement (z) explained in FIGS. 93and 94 is fed into and stored in the overall controller 127.

With reference to FIG. 95, the laser processing method in accordancewith the ninth embodiment of the present invention will now beexplained. FIG. 95 is a flowchart for explaining this laser processingmethod. The object to be processed 1 is a silicon wafer.

Step S101 is the same as step S101 of the first embodiment shown in FIG.15. Subsequently, the thickness of the object 1 is measured. Accordingto the result of measurement of thickness and the refractive index ofobject 1, the amount of movement (z) of object 1 in the Z-axis directionis determined (S103). This is the amount of movement of object 1 in theZ-axis direction with reference to the light-converging point of laserlight L positioned at the surface 3 of object 1 in order for thelight-converging point P of laser light L to be located within theobject 1. Namely, the position of light-converging point P in thethickness direction of object 1 is determined. The position oflight-converging point P is determined in view of the thickness andmaterial of object 1 and the like. In this embodiment, data of a firstmovement amount for positioning the light-converging point P near therear face within the object 1 and data of a second movement amount forpositioning the light-converging point P near the surface 3 within theobject 1 are used. A first molten processed region to be formed isformed by using the data of first movement amount. A second moltenprocessed region to be formed is formed by using the data of secondmovement amount. Data of these movement amounts are fed into the overallcontroller 127.

Steps S105 and S107 are the same as steps S105 and S107 in the firstembodiment shown in FIG. 15. The focal point data calculated by stepS107 is sent to the stage controller 115. According to the focal pointdata, the stage controller 115 moves the Z-axis stage 113 in the Z-axisdirection (S109). This positions the focal point of visible light of theobservation light source 117 at the surface 3. At this point of Z-axisstage 113, the focal point P of pulse laser light L is positioned at thesurface 3. Here, according to imaging data, the imaging data processor125 calculates enlarged image data of the surface of object 1 includingthe line 5 along which the object is intended to be cut. The enlargedimage data is sent to the monitor 129 by way of the overall controller127, whereby an enlarged image in the vicinity of the line 5 along whichthe object is intended to be cut is displayed on the monitor 129.

The data of first movement amount determined by step S103 has alreadybeen inputted to the overall controller 127, and is sent to the stagecontroller 115. According to this data of movement amount, the stagecontroller 115 moves the object 1 in the Z-axis direction by using theZ-axis stage 113 to a position where the light-converging point P oflaser light L is located within the object 1 (S111). This insideposition is near the rear face of the object 1.

Next, as in step S113 of the first embodiment shown in FIG. 15, a moltenprocessed region is formed within the object 1 so as to extend along theline 5 along which the object is intended to be cut (S113). The moltenprocessed region is formed near the rear face within the object 1.

Then, according to the data of second movement amount as in step S111,the object 1 is moved in the Z-axis direction by the Z-axis stage 113 toa position where the light-converging point P of laser light L islocated within the object 1 (S115). Subsequently, as in step S113, amolten processed region is formed within the object 1 (S117). In thisstep, the molten processed region is formed near the surface 3 withinthe object 1.

Finally, the object 1 is bent along the line 5 along which the object isintended to be cut, and thus is cut (S119). This divides the object 1into silicon chips.

Effects of the ninth embodiment of the present invention will beexplained. The ninth embodiment forms a plurality of modified regionsaligning in the direction of incidence, thereby increasing the number oflocations to become starting points when cutting the object 1. In thecase where the size of object 1 in the direction of incidence of laserlight is relatively large or where the object 1 is made of a material inwhich cracks are hard to grow from a modified region, for embodiment,the object 1 is hard to cut when only one modified region exists alongthe line 5 along which the object is intended to be cut. In such a case,forming a plurality of modified regions as in this embodiment can easilycut the object 1.

Tenth Embodiment

A tenth embodiment of the present invention controls the position of amodified region in the thickness direction of an object to be processedby adjusting the light-converging point of laser light in the thicknessdirection of the object.

This positional control will be explained in terms of a crack region byway of embodiment. FIG. 96 is a perspective view of an object to beprocessed 1 in which a crack region 9 is formed within the object 1 byusing the laser processing method in accordance with the tenthembodiment of the present invention. The light-converging point of pulselaser L is located within the object 1 through the surface (entranceface) 3 of the object with respect to the pulse laser light L. Thelight-converging point is adjusted so as to be located at asubstantially half thickness position in the thickness direction of theobject 1. When the object to be processed 1 is irradiated with the line5 along which the object is intended to be cut under these conditions, acrack region 9 is formed along a line 5 along which the object isintended to be cut at a half thickness position of the object 1 and itsvicinity.

FIG. 97 is a partly sectional view of the object 1 shown in FIG. 96.After the crack region 9 is formed, cracks 91 are naturally grown towardthe surface 3 and rear face 21. When the crack region 9 is formed at thehalf thickness position and its vicinity in the thickness direction ofthe object 1, the distance between the naturally growing crack 91 andthe surface 3 (rear face 21) can be made relatively long, forembodiment, in the case where the object 1 has a relatively largethickness. Therefore, apart to be cut extending along the line 5 alongwhich the object is intended to be cut in the object 1 maintains astrength to a certain extent. Therefore, when carrying out the step ofcutting the object 1 after terminating the laser processing, handlingthe object becomes easier.

FIG. 98 is a perspective view of an object to be processed 1 including acrack region 9 formed by using the laser processing method in accordancewith the tenth embodiment of the present invention as with FIG. 96. Thecrack region 9 shown in FIG. 98 is formed when the light-convergingpoint of pulse laser light L is adjusted so as to be located at aposition closer to the surface (entrance face) 3 than is a halfthickness position in the thickness direction of the object 1. The crackregion 9 is formed on the surface 3 side within the object 1. FIG. 99 isa partly sectional view of the object 1 shown in FIG. 98. Since thecrack region 9 is formed on the surface 3 side, naturally growing cracks91 reach the surface 3 or its vicinity. Hence, fractures extending alongthe line 5 along which the object is intended to be cut are likely tooccur in the surface 3, whereby the object 1 can be cut easily.

In the case where the surface 3 of the object 1 is formed withelectronic devices and electrode patterns in particular, forming thecrack region 9 near the surface 3 can prevent the electronic devices andthe like from being damaged when cutting the object 1. Namely, growingcracks 91 from the crack region 9 toward the surface 3 and rear face 21of the object 1 cuts the object 1. Cutting may be achieved by thenatural growth of cracks 91 alone or by artificially growing cracks 91in addition to the natural growth of crack 91. When the distance betweenthe crack region 9 and the surface 3 is relatively long, the deviationin the growing direction of cracks 91 on the surface 3 side becomesgreater. As a consequence, the cracks 91 may reach regions formed withelectronic devices and the like, thereby damaging the electronic devicesand the like. When the crack region 9 is formed near the surface 3, thedistance between the crack region 9 and the surface 3 is relativelyshort, whereby the deviation in growing direction of cracks 91 can bemade smaller. Therefore, cutting can be effected without damaging theelectronic devices and the like. When the crack region 9 is formed at alocation too close to the surface 3, the crack region 9 is formed at thesurface 3. As a consequence, the random form of the crack region 9itself appears at the surface 3, which causes chipping, therebydeteriorating the accuracy in breaking and cutting.

The crack region 9 can also be formed while the light-converging pointof pulse laser light L is adjusted so as to be located at a positionfarther from the surface 3 than is a half thickness position in thethickness direction of the object 1. In this case, the crack region 9 isformed on the rear face 21 side within the object 1.

As with FIG. 96, FIG. 100 is a perspective view of the object 1including crack regions formed by using the laser processing method inaccordance with the tenth embodiment of the present invention. The crackregion 9 in the X-axis direction shown in FIG. 100 is formed when thelight-converging point of pulse laser light L is adjusted so as to belocated at a position farther from the surface (entrance face) 3 than isa half thickness position in the thickness direction of the object 1.The crack region 9 in the Y-axis direction is formed when thelight-converging point of pulse laser light L is adjusted so as to belocated at a position closer to the surface 3 than is the half thicknessposition in the thickness direction of the object 1. The crack region 9in the X-axis direction and the crack region 9 in the Y-axis directioncross each other three-dimensionally.

When the object 1 is a semiconductor wafer, for embodiment, a pluralityof crack regions 9 are formed in parallel in each of the X- and Y-axisdirections. This forms the crack regions 9 like a lattice in thesemiconductor wafer, whereas the latter is divided into individual chipswhile using the lattice-like crack regions as starting points. When thecrack region 9 in the X-axis direction and the crack region 9 in theY-axis direction are located at the same position in the thicknessdirection of the object 1, there occurs a location where the crackregion 9 in the X-axis direction and the crack region 9 in the Y-axisdirection intersect each other at right angles. At the location wherethe crack regions 9 intersect each other at right angles, they aresuperposed on each other, which makes it difficult for the cross sectionin the X-axis direction and the cross section in the Y-axis direction tointersect each other at right angles with a high accuracy. This inhibitsthe object 1 from being cut precisely at the intersection.

When the position of the crack region 9 in the X-axis direction and theposition of the crack region 9 in the Y-axis direction differ from eachother in the thickness direction of the object 1 as shown in FIG. 100,the crack region 9 in the X-axis direction and the crack region 9 in theY-axis direction can be prevented from being superposed on each other.This enables precise cutting of the object 1.

In the crack region 9 in the X-axis direction and the crack region 9 inthe Y-axis direction, the crack region 9 to be formed later ispreferably formed closer to the surface (entrance face) 3 than is thecrack region 9 formed earlier. If the crack region 9 to be formed lateris formed closer to the rear face 21 than is the crack region 9 formedearlier, the pulse laser light L irradiated when forming the crackregion 9 to be formed later is scattered by the crack region 9 formedearlier at the location where the cross section in the X-axis directionand the cross section in the Y-axis direction intersect each other atright angles. This forms deviations between the size of a part formed ata position to become the above-mentioned intersecting location and thesize of a part formed at another position in the crack region 9 to beformed later. Therefore, the crack region 9 to be formed later cannot beformed uniformly.

When the crack region 9 to be formed later is formed closer to thesurface 3 than is the crack region 9 formed earlier, by contrast,scattering of the pulse laser light L does not occur at a position tobecome the above-mentioned intersecting location, whereby the crackregion 9 to be formed later can be formed uniformly.

As explained in the foregoing, the tenth embodiment of the presentinvention adjusts the position of light-converging point of laser lightin the thickness direction of an object to be processed, thereby beingable to control the position of a modified region in the thicknessdirection of the object. Changing the position of light-converging pointin view of the thickness and material of the object to be processed andthe like enables laser processing in conformity to the object.

Though the fact that the position of a modified region can be controlledis explained in the case of a crack region, the same holds in moltenprocessed regions and refractive index change regions. Though theexplanation relates to pulse laser light, the same holds for continuouswave laser light.

The laser processing apparatus in accordance with the tenth embodimentof the present invention has a configuration similar to the laserprocessing apparatus 100 in accordance with the first embodiment shownin FIG. 14. In the tenth embodiment, the Z-axis stage 113 adjusts theposition of light-converging point Pin the thickness direction of object1. This can adjust the light-converging point P so as to locate it at aposition closer to or farther from the entrance face (surface 3) than isa half thickness position in the thickness direction of the object 1 orat a substantially half thickness position, for embodiment. Theseadjustment operations and the placement of the light-converging point oflaser light within the object can also be achieved by moving thelight-converging lens 105 in the Z-axis direction. Since there are caseswhere the object 1 moves in the thickness direction thereof and wherethe light-converging lens 105 moves in the thickness direction of theobject 1 in the present invention, the amount of movement of the object1 in the thickness direction of the object 1 is defined as a firstrelative movement amount or a second relative movement amount.

The adjustment of light-converging point P in the thickness direction ofthe object to be processed caused by the Z-axis stage is the same asthat in the ninth embodiment explained with reference to FIG. 93 andFIG. 94.

The imaging data processor 125 calculates focal point data for locatingthe focal point of visible light generated by the observation lightsource 117 on the surface 3 according to the imaging data in the tenthembodiment as well. According to this focal point data, the stagecontroller 115 controls the movement of the Z-axis stage 113, so as tolocate the focal point of visible light at the surface 3. The laserprocessing apparatus 1 is adjusted such that the light-converging pointP of laser light L is located at the surface 3 at the position of Z-axisstage 113 where the focal point of visible light is located at thesurface 3. Hence, the focal point data is an embodiment of secondrelative movement amount of the object 1 in the thickness directionthereof required for locating the light-converging point P at thesurface (entrance face) 3. The imaging data processor 125 has a functionof calculating the second relative movement amount.

Data of the movement amount (z) explained with reference to FIGS. 93 and94 is fed into and stored in the overall controller 127. Namely, theoverall controller 127 has a function of storing data of the relativemovement amount of the object to be processed 1 in the thicknessdirection of the object 1. The overall controller 127, stage controller115, and Z-axis stage 113 adjust the position of light-converging pointof pulse laser light converged by the light-converging lens within therange of thickness of the object 1.

The laser processing method in accordance with the tenth embodiment willbe explained with reference to the laser processing apparatus inaccordance with the first embodiment shown in FIG. 14 and the flowchartfor the laser processing method in accordance with the first embodimentshown in FIG. 15. The object to be processed 1 is a silicon wafer.

Step S101 is the same as step S101 of the first embodiment shown in FIG.15. Subsequently, as in step S103 of the first embodiment shown in FIG.15, the thickness of object 1 is measured. According to the result ofmeasurement of thickness and the refractive index, the amount ofmovement (z) in the Z-axis direction of object 1 is determined (S103).This is the amount of movement of object 1 in the Z-axis direction withreference to the light-converging point of laser light L positioned atthe surface 3 of object 1 required for positioning the light-convergingpoint P of laser light L within the object 1. Namely, the position oflight-converging point P in the thickness direction of object 1 isdetermined. The amount of movement (z) in the Z-axis direction is oneembodiment of data of relative movement of the object 1 in the thicknessdirection thereof. The position of light-converging point P isdetermined in view of the thickness and material of the object 1,effects of processing (e.g., easiness to handle and cut the object), andthe like. This data of movement amount is fed into the overallcontroller 127.

Steps S105 and S107 are similar to steps S105 and S107 of the firstembodiment shown in FIG. 15. The focal point data calculated by stepS107 is data of a second movement amount in the Z-axis direction ofobject 1.

This focal point data is sent to the stage controller 115. According tothis focal point data, the stage controller 115 moves the Z-axis stage113 in the Z-axis direction (S109). This positions the focal point ofvisible light of the observation light source 117 at the surface 3. Atthis position of Z-axis stage 113, the light-converging point P of pulselaser light L is positioned at the surface 3. According to imaging data,the imaging data processor 125 calculates enlarged image data of thesurface of object 1 including the line 5 along which the object isintended to be cut. This enlarged image data is sent to the monitor 129by way of the overall controller 127, whereby an enlarged image near theline 5 along which the object is intended to be cut is displayed on themonitor 127.

Data of the relative movement amount determined by step S103 has alreadybeen inputted to the overall controller 127, and is sent to the stagecontroller 115. According to this data of movement amount, the stagecontroller 115 causes the Z-axis stage 113 to move the object 1 in theZ-axis direction at a position where the light-converging point P oflaser light is located within the object 1 (S111).

Steps S113 and S115 are similar to steps S113 and S115 shown in FIG. 15.The foregoing divides the object 1 into silicon chips.

Effects of the tenth embodiment of the present invention will beexplained. The tenth embodiment irradiates the object to be processed 1with pulse laser light L while adjusting the position oflight-converging point P in the thickness direction of object 1, therebyforming a modified region. This can control the position of a modifiedregion in the thickness direction of object 1. Therefore, changing theposition of a modified region in the thickness direction of object 1according to the material and thickness of object 1, effects ofprocessing, and the like enables cutting in conformity to the object 1.

Eleventh Embodiment

A Eleventh embodiment of the present invention will now be explained.The laser processing method in accordance with the eleventh embodimentcomprises a modified region forming step (first step) of forming amodified region caused by multiphoton absorption within an object to beprocessed, and a stress step (second step) of generating a stress at apart where the object is cut. In the eleventh embodiment, the same laserlight irradiation is carried out in the modified region forming step andstress step. Therefore, a laser processing apparatus, which wasexplained above, emits laser light twice under the same condition in themodified region forming step and stress step, respectively.

With reference to FIGS. 14 and 101, the laser processing method inaccordance with the eleventh embodiment will now be explained. FIG. 101is a flowchart for explaining the laser processing method.

Steps S101, S103, S105, S107, S109 and S111 shown in FIG. 101, are thesame as theses shown in FIG. 15, and therefore, the detailedexplanations of the Steps S101, S103, S105, S107, S109 and S111 areomitted.

After Step S111, laser light L is generated from the laser light source101, so as to irradiate the line 5 along which the object is intended tobe cut 5 in the surface 3 of the object 1 therewith. FIG. 102 is asectional view of the object 1 including a crack region 9 during laserprocessing in the modified region forming step. Since thelight-converging point P of laser light L is positioned within theobject 1 as depicted, the crack region 9 is formed only within theobject 1. Subsequently, the X-axis stage 109 and Y-axis stage 111 aremoved along the line to be cut 5, so as to form the crack region 9within the object 1 along the line 5 along which the object is intendedto be cut (S1113).

After the modified region is formed, the crack region 9 is irradiatedwith the laser light L having for example, wavelength of 1064 nm (YAGlaser) along the line 5 along which the object is intended to be cut inthe surface 3 of the object 1 again under the same condition (i.e., thelight-converging point P is located in the crack region 9 that is amodified region). The laser light L has a transparent characteristics tonon-molten processed region of the object, that is, except for themolten processed region of the object, and a high absorptioncharacteristics to the molten processed region comparing with thenon-molten processed region. As a consequence, the absorption of laserlight L due to scattering by the crack region 9 or the like or thegeneration of multiphoton absorption in the crack region 9 heats theobject 1 along the crack region 9, thereby generating a stress such as athermal stress due to a temperature difference (S1114). FIG. 103 is asectional view of the object 1 including the crack region 9 during laserprocessing in the stress step. As depicted, the crack is further grownby the stress step while using the crack region 9 as a start point, soas to reach the surface 3 and rear face 21 of the object 1, thus forminga cut section 10 in the object 1, whereby the object 1 is cut (S1115).As a consequence, the object 1 is divided into chips.

Though the eleventh embodiment carries out the same laser lightirradiation as that of the modified region forming step in the stressstep, it will be sufficient if laser light transmittable through anunmodified region which is a region not formed with a crack region inthe object to be processed but more absorbable by the crack region thanby the unmodified region is emitted. This is because of the fact thatthe laser light is hardly absorbed at the surface of the object, whereasthe object is heated along the crack region, whereby a stress such as athermal stress due to a temperature difference occurs in this case aswell.

Though the eleventh embodiment relates to a case where a crack region isformed as the modified region, the same applies to cases where theabove-mentioned molten processed region and refractive index changeregion are formed as the modified region, whereby a stress can occurupon irradiation with laser light in the stress step, so as to generateand grow a crack while using the molten processed region and refractiveindex change region as a start point and thereby cut the object.

Even when the crack grown by the stress step while using the modifiedregion as a start point fails to reach the surface and rear face of theobject in the case where the object has a large thickness or the like,the object can be broken and cut by applying an artificial force such asa bending stress or shearing stress thereto. This artificial force canbe kept smaller, whereby unnecessary fractures deviating from the lineto be cut can be prevented from occurring in the surface of the object.

Effects of the eleventh embodiment will now be explained. In themodified region forming step of this embodiment, the line 5 along whichthe object is intended to be cut is irradiated with pulse laser light Lwhile locating the light-converging point P within the object to beprocessed 1 under a condition causing multiphoton absorption. Also, theX-axis stage 109 and Y-axis stage 111 are moved, so as to shift thelight-converging point P along the line 5 along which the object isintended to be cut. This forms a modified region (e.g., crack region,molten processed region, or refractive index change region) within theobject 1 along the line 5 along which the object is intended to be cut.When an object to be processed has a start point in a part to be cut,the object can be broken and cut with a relatively small force. In thestress step of the eleventh embodiment, the same laser light irradiationas that of the modified region forming step is carried out in the stressstep, so as to generate a stress such as a thermal stress due to atemperature difference. As a consequence, the object 1 can be cut by arelatively small force, e.g., a stress such as a thermal stress due to atemperature difference. Therefore, the object 1 can be cut withoutgenerating unnecessary fractures deviating from the line 5 along whichthe object is intended to be cut in the surface 3 of the object 1.

Since the object 1 is irradiated with the pulse laser light L whilelocating the light-converging point P within the object 1 under acondition causing multiphoton absorption in the modified region formingstep, the pulse laser light L is transmitted there through and is hardlyabsorbed at the surface 3 of the object 1 in the eleventh embodiment. Inthe stress step, the same laser light irradiation as that of themodified region forming step is carried out. Therefore, the surface 3does not incur damages such as melt caused by irradiation with laserlight.

As explained in the foregoing, the eleventh embodiment can cut theobject 1 without generating unnecessary fractures deviating from theline 5 along which the object is intended to be cut or melt in thesurface 3 of the object 1. Therefore, in the case where the object 1 isa semiconductor wafer, for embodiment, semiconductor chips can be cutout from the semiconductor wafer without generating unnecessaryfractures deviating from lines along which the object is intended to becut or melt in the semiconductor chips. The same holds in objects to beprocessed having a surface formed with electrode patterns, and thosehaving a surface formed with electronic devices such as piezoelectricdevice wafers and glass substrates formed with display devices such asliquid crystals. Hence, this embodiment can improve the yield ofproducts (e.g., semiconductor chips, piezoelectric device chips, displaydevices such as liquid crystals) made by cutting objects to beprocessed.

Also, in the eleventh embodiment, the line 5 along which the object isintended to be cut in the surface 3 of the object 1 does not melt,whereby the width of the line 5 along which the object is intended to becut (which is the gap between regions to become semiconductor chips inthe case of a semiconductor wafer, for embodiment) can be reduced. Thiscan increase the number of products prepared from a single object to beprocessed 1, and improve the productivity of products.

Since laser light is used for cutting and processing the object 1, theeleventh embodiment enables processing more complicated than that indicing with a diamond cutter. For the eleventh embodiment, cutting andprocessing can be carried out even when lines 5 along which the object 1is intended to be cut 5 have a complex form as shown in FIG. 16 also.

The laser processing method in accordance with the eleventh embodimentaccording to the present invention can cut an object to be processedwithout generating melt or unnecessary fractures deviating from the lineto be cut in the surface of the object. Therefore, the yield andproductivity of products (e.g., semiconductor chips, piezoelectricdevice chips, and display devices such as liquid crystals) manufacturedby cutting objects to be processed can be improved.

Besides, in the above eleventh embodiments, the crack which is grownfrom the crack region 9 in the stress step reaches the surface 3 andrear face 21 of the object 1, but the crack which is grown from thecrack region 9 in the stress step the laser light L may be grown so asnot to reach the surface 3 and rear face 21 of the object.

Twelfth Embodiment

The twelve embodiment according to the present invention will now beexplained. The laser processing method in accordance with the twelfthembodiment comprises a modified region forming step of forming amodified region caused by multiphoton absorption within an object to beprocessed, and a stress step of generating a stress at a part where theobject is cut, as similar to the eleventh embodiment.

A laser processing apparatus for the twelfth embodiment is the same asthat of the first embodiment as shown in FIG. 14, and the detailedexplanation of the laser processing apparatus is omitted.

An absorbable laser irradiating apparatus used in the stress step of thetwelfth embodiment employs the same configuration as that of theabove-mentioned laser processing apparatus 100 as shown in FIG. 14except for the laser light source and diachronic mirror. The laser lightsource in the absorbable laser irradiating apparatus uses CO₂ laser witha wavelength of 10.6 μm for generating continuous wave laser light. Thisis because of the fact that it is absorbable by the object 1 to beprocessed, which is a Pyrex glass wafer. Alternatively, the laser diodemay be used as a light source for generating the absorbable laser lightwith a wavelength of 808 nm, 14 W as output power and beam size of about200 μm. The laser light generated by such laser light source has aabsorption characteristics to the object 1 and will hereinafter bereferred to as “absorbable laser light”. Here, its beam quality isTEM₀₀, whereas its polarization characteristic is that of linearpolarization. This laser light source has an output of 10 W or less inorder to attain such an intensity that the object to be processed 1 isheated but not melted thereby. The diachronic mirror of the absorbablelaser irradiating apparatus has a function of reflecting the absorbablelaser light, and is arranged so as to change the orientation of theoptical axis of absorbable laser light by 90°.

With reference to FIGS. 14 and 104, the laser processing method inaccordance with the twelfth embodiment will now be explained. FIG. 104is a flowchart for explaining the laser processing method.

Steps S101, S103, S105, S107, S109 and S111 shown in FIG. 104, are thesame as theses shown in FIG. 15, and therefore, the detailedexplanations of the Steps S101, S103, S105, S107, S109 and S111 areomitted.

Firstly, as shown in FIG. 104, steps S101 and S103 are executed and nextstep S104 is executed. In the step S104, the object 1 is mounted on themounting table 107 of the laser processing apparatus 100 (S104). Nextsteps S105, S107, S109, and S111 are executed. After Step 111 of FIG.104, laser light L is generated from the laser light source 101, so asto irradiate the line 5 along which the object is intended to be cut inthe surface 3 of the object 1 therewith. FIG. 102 is a sectional view ofthe object 1 including a crack region 9 during laser processing in themodified region forming step. Since the light-converging point P oflaser light L is positioned within the object 1 as depicted, the crackregion 9 is formed only within the object 1. Subsequently, the X-axisstage 109 and Y-axis stage 111 are moved along the line 5 along whichthe object is intended to be cut, so as to form the crack region 9within the object 1 along the line 5 along which the object is intendedto be cut (S1213).

After the modified region is formed by the laser processing apparatus100, the object 1 is transferred to the mounting table 107 of theabsorbable laser irradiating apparatus, so as to be mounted thereon(S1215). The object 1 does not break into pieces, since the crack region9 in the modified region forming step is formed only therewithin, andthus can easily be transferred.

The object 1 is illuminated in step 1217, focal point data forpositioning the focal point of visible light from the observation lightsource at the surface 3 of the object 1 is calculated in step 1219, andthe object 1 is moved in the Z-axis direction so as to position thefocal point at the surface 3 of the object 1 in step 1221, therebylocating the light-converging point of absorbable laser light L2 at thesurface 3 of the object. Here, details of operations in the steps 1217,1219, and 1221 are similar to those of steps 105, 107, and 109 in theabove-mentioned laser processing apparatus 100.

Next, absorbable laser light L2 is generated from the laser light sourceof the absorbable laser irradiating apparatus, so as to irradiate theline 5 along which the object is intended to be cut in the surface 3 ofthe object 1 therewith. Here, the vicinity of the line 5 along which theobject is intended to be cut may be irradiated as well. Then, the X-axisstage and Y-axis stage of the absorbable laser irradiating apparatus aremoved along the line 5 along which the object is intended to be cut, soas to heat the object 1 along the line 5 along which the object isintended to be cut, thereby generating a stress such as thermal stresscaused by a temperature difference at a part where the object 1 is cutalong the line 5 along which the object is intended to be cut (S1223).Here, since the absorbable laser has such an intensity that the object 1is heated but not melted thereby, the surface of the object does notmelt.

FIG. 105 is a sectional view of the object 1 including the crack region9 during laser processing in the stress step. As depicted, uponirradiation with absorbable laser light, the crack further grows whileusing the crack region 9 as a start point, so as to reach the surface 3and rear face 21 of the object 1, thus forming a cut section 10 in theobject 1, whereby the object 1 is cut (S1225). As a consequence, theobject 1 is divided into silicon chips.

Though the twelfth embodiment relates to a case where a crack region isformed as the modified region, the same applies to cases where theabove-mentioned molten processed region and refractive index changeregion are formed as the modified region, whereby a stress can occurupon irradiation with absorbable laser light, so as to generate and growa crack while using the molten processed region and refractive indexchange region as a start point and thereby cut the object.

Even when the crack grown by the stress step while using the modifiedregion as a start point fails to reach the surface and rear face of theobject in the case where the object has a large thickness or the like,the object can be broken and cut by applying an artificial force such asa bending stress or shearing stress thereto. This artificial force canbe kept smaller, whereby unnecessary fractures deviating from the lineto be cut can be prevented from occurring in the surface of the object.

Effects of the twelfth embodiment will now be explained. In the modifiedregion forming step of this embodiment, the line 5 along which theobject is intended to be cut is irradiated with pulse laser light Lwhile locating the light-converging point P within the object to beprocessed 1 under a condition causing multiphoton absorption. Also, theX-axis stage 109 and Y-axis stage 111 are moved, so as to shift thelight-converging point P along the line 5 along which the object isintended to be cut. This forms a modified region (e.g., crack region,molten processed region, or refractive index change region) within theobject 1 along the line 5 along which the object is intended to be cut.When an object to be processed has a start point in a part to be cut,the object can be broken and cut with a relatively small force. In thestress step of this embodiment, the object 1 is irradiated withabsorbable laser light along the line 5 along which the object isintended to be cut, so as to generate a stress such as a thermal stressdue to a temperature difference. As a consequence, the object 1 can becut by a relatively small force, e.g., a stress such as a thermal stressdue to a temperature difference. Therefore, the object 1 can be cutwithout generating unnecessary fractures deviating from the line 5 alongwhich the object is intended to be cut in the surface 3 of the object 1.

Since the object 1 is irradiated with the pulse laser light L whilelocating the light-converging point P within the object 1 under acondition causing multiphoton absorption in the modified region formingstep, the pulse laser light L is transmitted there through and is hardlyabsorbed at the surface 3 of the object 1 in this embodiment. In thestress step, the absorbable laser light has such an intensity that theobject 1 is heated but not melted thereby. Therefore, the surface 3 doesnot incur damages such as melt caused by irradiation with laser light.

As explained in the foregoing, this embodiment can cut the object 1without generating unnecessary fractures deviating from the line 5 alongwhich the object is intended to be cut or melt in the surface 3 of theobject 1. Therefore, in the case where the object 1 is a semiconductorwafer, for embodiment, semiconductor chips can be cut out from thesemiconductor wafer without generating unnecessary fractures deviatingfrom lines along which the object is intended to be cut or melt in thesemiconductor chips. The same holds in objects to be processed having asurface formed with electrode patterns, and those having a surfaceformed with electronic devices such as piezoelectric device wafers andglass substrates formed with display devices such as liquid crystals.Hence, this embodiment can improve the yield of products (e.g.,semiconductor chips, piezoelectric device chips, display devices such asliquid crystals) made by cutting objects to be processed.

Also, in this embodiment, the line 5 along which the object is intendedto be cut in the surface 3 of the object 1 does not melt, whereby thewidth of the line 5 along which the object is intended to be cut (whichis the gap between regions to become semiconductor chips in the case ofa semiconductor wafer, for embodiment) can be reduced. This can increasethe number of products prepared from a single object to be processed 1,and improve the productivity of products.

Since laser light is used for cutting and processing the object 1, thisembodiment enables processing more complicated than that in dicing witha diamond cutter. For embodiment, cutting and processing can be carriedout even when line 5 along which the object is intended to be cut have acomplex form as shown in FIG. 16.

The laser processing method of the twelfth embodiment according to thepresent invention can cut an object to be processed without generatingmelt or unnecessary fractures deviating from the line to be cut in thesurface of the object. Therefore, the yield and productivity of products(e.g., semiconductor chips, piezoelectric device chips, and displaydevices such as liquid crystals) manufactured by cutting objects to beprocessed can be improved.

Besides, in the above eleventh embodiments, the crack which is grownfrom the crack region 9 in the stress step reaches the surface 3 andrear face 21 of the object 1, but the crack which is grown from thecrack region 9 in the stress step the laser light L may be grown so asnot to reach the surface 3 and rear face 21 of the object.

Thirteenth Embodiment

The thirteenth embodiment according to the present invention will now beexplained. The laser processing method in accordance with the thirteenthembodiment comprises attaching step of adhesively attaching an object tobe processed to an adhesive and expansive sheet, a modified regionforming step of forming a modified region in the object, andcutting/separation step of cutting the object at the modified regionthereof and separating the cut parts of the object so as to make thespace there between.

The above modified region forming step of the thirteenth embodiments maybe any one of the first to twelfth embodiments stated above. Further, inthe modified region forming step, the object may be cut at the modifiedregion. In this case that the object is cut at the modified region inthe modified region forming step, in the separation step, the cut partsof the object are spaced to each other by a predetermined distance byexpansion of the adhesive and expansion sheet. Alternatively, when inthe modified region forming step, although the modified region is formedin the body as a molten processed region, the object is not cut, in theseparation step, the object is cut and the cut parts of the object areseparated to each other with a predetermined space therebetween.

FIG. 106 shows a film expansion apparatus 200 and the apparatus 200 hasa ring shape holder 201 and a column like expander 203. The adhesive andexpansive sheet on which the object to be cut is attached is set to thering shape holder 201. After setting of the adhesive and expansive sheet204 on the ring shape holder 201 at peripheral edge of the sheet, themodified region is formed in the object along a line along which theobject is intended to be cut. After the formation of the modified regionin the object, the column like expander 203 is moved up against theadhesive and expansive sheet 204 so that a part of the sheet is pushedupward as shown in FIG. 107. The movement of the part of the sheet 204causes the expansion of the sheet along a lateral direction thereof sothat the sheet 204 is expanded as shown in FIG. 107. As the result ofthe expansion of the sheet 204, the parts of the object which is cut inthe modified region forming step are separated to each other with apredetermined space therebetween. So, the pick up of the parts of theobject from the adhesive and expansive sheet 204 is performed easily andsurely.

When the object is not cut in the modified region formation step, theexpansion of the sheet 204 caused by the upward movement of the expander203 causes the separation of the object into parts of the object in themodified region and thereafter the cut parts of the object are separatedto each other with a predetermined space therebetween.

The laser processing method and apparatus in accordance with the presentinvention can cut an object to be processed without generating melt orfractures deviating from lines along which the object is intended to becut on a surface of the object. Therefore, the yield and productivity ofproducts (e.g., semiconductor chips, piezoelectric device chips, anddisplay devices such as liquid crystal) prepared by cutting objects tobe processed can be improved.

The basic Japanese Application No. 2000-278306 filed on Sep. 13, 2000and No. 2001-278768 filed on Sep. 13, 2001 and PCT Application No.PCT/JP01/07954 filed on Sep. 13, 2001 are hereby incorporated byreference.

From the invention thus described, it will be obvious that theembodiments of the invention may be varied in many ways. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended for inclusion within the scope of the followingclaims.

1-44. (canceled)
 45. A method of cutting a substrate, the methodcomprising steps of: irradiating a substrate with pulsed laser lighthaving a converging point positioned within the substrate in order toform a molten processed spot within the substrate at the convergingpoint; and performing the irradiating step at multiple locations along aline along which the substrate is to be cut in order to form a pluralityof molten processed spots within the substrate at converging points ofthe pulsed laser light, respectively, without melting a pulsed laserlight incident surface of the substrate, wherein the molten processedspots are formed so that the molten processed spots overlap each otherand make up a molten processed region formed only within the substratewhich functions as a starting point for cutting the substrate along theline along which the substrate is to be cut; wherein the starting pointis formed in the substrate only by the laser irradiation, and a crack isgrown from the starting point in a thickness direction of the substrateso that the crack reaches to a front and back surface of the substrateand the substrate is thereby cut.
 46. A method of cutting a substrate,the method comprising steps of: irradiating a substrate with pulsedlaser light having a converging point positioned within the substrate;and performing the irradiating step at multiple locations along a linealong which the substrate is to be cut in order to form a plurality ofrefractive index change spots within the substrate at converging pointsof the pulsed laser light, respectively, without melting a pulsed laserlight incident surface of the substrate, wherein the refractive indexchange spots are formed so that the refractive index change spotsoverlap each other and make up a refractive index change region formedonly within the substrate which functions as a starting point forcutting the substrate along the line along which the substrate is to becut; wherein the starting point is formed in the substrate only by thelaser irradiation, and a crack is grown from the starting point in athickness direction of the substrate so that the crack reaches to afront and back surface of the substrate and the substrate is therebycut.
 47. The method according to claim 45, wherein a plurality ofmodified regions are formed along each of first lines along which thesubstrate is to be cut, a plurality of regions are formed along each ofsecond lines along which the substrate is to be cut, the second linescrossing the first lines, and after formation of the modified regionshas been performed, the substrate is cut in into at least one piecehaving a chip shape.
 48. The method according to claim 46, wherein aplurality of modified regions are formed along each of first lines alongwhich the substrate is to be cut, a plurality of regions are formedalong each of second lines along which the substrate is to be cut, thesecond lines crossing the first lines, and after formation of themodified regions has been performed, the substrate is cut into at leastone piece having a chip shape.
 49. A method of processing a wafer-likeobject, the method comprising steps of: irradiating the object withpulsed laser light having a converging point within the object, whereinthe irradiating step is performed at multiple locations in order to forma plurality of modified spots at converging points of the pulsed laserlight along a line along which the object is to be cut in order to forma modified region made up of the modified spots which functions as astarting point for cutting the object; wherein the converging pointshave a pitch representing a distance between adjacent converging pointsalong the line along which the object is to be cut, wherein the modifiedspots have a dimension in a direction along the line along which theobject is to be cut, and wherein the pitch of the converging points isless than the dimension of the modified spots in the direction along theline along which the object is to be cut.
 50. The method according toclaim 49, wherein each modified spot is a molten processed spot and themodified region is a molten processed region.
 51. The method accordingto claim 49, wherein each modified spot is a refractive index changespot and the modified region is a refractive index change region. 52.The method according to claim 49, wherein a plurality of modifiedregions are formed along each of first lines along which the substrateis to be cut, a plurality of regions are formed along each of secondlines along which the substrate is to be cut, the second lines crossingthe first lines, and after formation of the modified regions has beenperformed, the substrate is cut into at least one piece having a chipshape.
 53. A method of manufacturing a semiconductor device formed usinga substrate cutting method, the manufacturing method comprising thesteps of: irradiating a substrate with laser light comprising a pulsedlaser light having a pulse width larger than 1 μs at a converging pointwithin the substrate, so that the converging point of the pulsed laserlight is positioned within the substrate and a peak power of the laserlight at the converging point is not less than 1×10⁸ (W/cm²), in orderto form a molten processed spot within the substrate at the convergingpoint; and performing the irradiating step at multiple locations along aline along which the substrate is to be cut in order to form a pluralityof molten processed spots within the substrate at converging points ofthe pulsed laser light respectively, without melting a pulsed laserlight incident surface of the substrate, wherein the molten processedspots are formed so that the molten processed spots overlap each otherand make up a molten processed region formed only within the substratewhich functions as a starting point for cutting the substrate along theline along which the substrate is to be cut; wherein the starting pointis formed in the substrate only by the laser irradiation, and a crack isgrown from the starting point in a thickness direction of the substrateso that the crack reaches to a front and back surface of the substrateso that the substrate is cut, and the substrate is thereby cut in orderto provide at least one manufactured semiconductor device.
 54. A methodof manufacturing a semiconductor device formed using a substrate cuttingmethod, the manufacturing method comprising the steps of: irradiating asubstrate with a laser light comprising a pulsed laser light having apulse width larger than 1 μs at a converging point within the substrate,wherein the irradiating step is performed at multiple locations in orderto form a plurality of modified spots at converging points of the pulsedlaser light along a line along which the object is to be cut in order toform a modified region made up of the modified spots which functions asa starting point for cutting the object, wherein the converging pointshave a pitch representing a distance between adjacent converging pointsalong the line along which the object is to be cut, wherein the modifiedspots have a dimension in a direction along the line along which theobject is to be cut, wherein the pitch of the converging points is lessthan the dimension of the modified spots in the direction along the linealong which the object is to be cut; and cutting the substrate in orderto provide at least one manufactured semiconductor device, wherein thecutting step comprises cutting the substrate at least along the linealong which the object is to be cut.
 55. The method according to claim53, wherein a plurality of molten processed regions are formed alongeach of first lines along which the substrate is to be cut, a pluralityof molten processed regions are formed along each of second lines alongwhich the substrate is to be cut, the second lines crossing the firstlines, and after formation of the molten processed regions has beenperformed, the substrate is cut into at least one piece having a chipshape.
 56. The method according to claim 54, wherein each modified spotis a molten processed spot and the modified region is a molten processedregion.
 57. The method according to claim 54, wherein a plurality ofmodified regions are formed along each of first lines along which thesubstrate is to be cut, a plurality of regions are formed along each ofsecond lines along which the substrate is to be cut, the second linescrossing the first lines, and after formation of the modified regionshas been performed, the substrate is cut into at least one piece havinga chip shape.
 58. The method according to claim 45, wherein the pulsedlaser light has a pulse width larger than 1 μs at the converging pointand a peak power of the laser light at the converging point is not lessthan 1×10⁸ (W/cm²).
 59. The method according to claim 46, wherein thepulsed laser light has a pulse width larger than 1 ns at the convergingpoint and a peak power of the laser light at the converging point is notless than 1×10⁸ (W/cm2).
 60. The method according to claim 49, whereinthe pulsed laser light has a pulse width larger than 1 μs at theconverging point and a peak power of the laser light at the convergingpoint is not less than 1×10⁸ (W/cm²).